Absolutely yes! I ride almost exclusively indoors even during the summer due to work schedule and family responsibilities, and I had the fastest bike split in 3 of my 4 races this year. I have gotten to the point where I can't wait for my Zwift races once every week or two because of the absolute suffering and fun I get from them. It's a great way to keep your competitive juices flowing all year. In fact it's hard to find a good time for an off season because I want to do well in the winter Zwift racing season. The only time I ride outside is for the relaxing fall long group rides because I love the atmosphere.

As far as a smart trainer goes, I've never tried one but I personally enjoy just using my Powertap so I can ride a steady cadence up climbs or on descents. When I'm on the trainer I really don't want to spin at 120 or grind at 60 rpm very much. Plus with the PT my numbers transfer to the road easily. In terms of $$, for someone like me with basically no discretionary income, a smart trainer seems like a pointless luxury item that provides less benefit than a power meter you can take on the road and race with.

I would definitely recommend using direct power measurement though, I've tested the power curve from virtual power and my PT and found that virtual power has almost no correlation to the real thing. Inexplicably they don't even follow the same curve most of the time.

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Powertap / Cycleops / Saris

I used to use CycleOps' online platform called Virtual Training and they had Ironman courses on there with GPS data for grade changes on your trainer. Some were good with real video recorded to match the course others were so-so with no video. I think the platform has been renamed Rouvy.

I just signed up for Zwift. I also use TR. Zwift does have a learning curve. I don't give two shits about the social aspect of Zwift but doing races is an amazing way to push yourself. For more structured workouts I use TR.

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The curious task of economics is to demonstrate to men how little they really know about what they imagine they can design.

The answer seems to be yes...but what about with a dumb trainer?

No, and no. I don't like exercising of any kind indoors (with the exception of swimming in a natatorium). If exercising indoors doesn't bother you, I think it would be fine.

I prefer trainerroad and their specific plans to zwift. I'd much rather take a "get in, get out" approach with my indoor training but to each their own.

Trainer road and zwift guy here. Started with tr 4 years ago and zwift 2+ years ago when it was free. Have very slowly migrated from tr to zwift. I like the programs and structure of tr. However the past 10 months I’ve joined a virtual team and am really enjoying the team workouts and races on zwift. Team workouts are brutal: sprints, climbs, and some sweet spot done on flat, hills, and rollers in zwift.

I’m pushing my max just to stay with the group, in the redline at 176 bpm when the group surges and I somehow dig in to bridge up at 181 bpm,... what an addictive sensation. I could never push and repeat like that on tr but in zwift with all the banter, testosterone, and not wanting to get dropped, it’s just a step up to the next level.

With the right group and program, combined with terrain and physics engines/drafting, zwift is the future. It only a matter of time before the structured workouts and programs are further enhanced and implemented on zwift. In the future, tr is like blockbuster video, zwift is netflix. Sorry guys.

I've been using Zwift with a dumb trainer (KK Road Machine) for well over a year now. I don't have a power meter, I just use virtual power. There are a handful of good dumb trainers, including the Road Machine that work great with Zwift and they're the cheapest way to get up and running. I also really like the feel of a good fluid trainer. I had a go of a smart trainer with it and wasn't overly impressed but it wasn't a high end one like a Flux, Neo or Kickr so maybe they're a different experience.
Smart trainers give you two main extras: ERG mode and slope simulation. I don't particularly like the idea of ERG mode. Psychologically I don't think it's ideal. I've tried it and it works okay but I'd rather control my power for myself with my legs and gear selection. So ERG mode is not a selling point for me. Slope simulation might be nice when using Zwift so long as it's fairly realistic. I'm in the habit of dropping a gear to increase the load and reduce cadence on climbs in Zwift. Or if I'm doing a structured session I ignore the terrain from the perspective of effort and cadence/gear selection.That works fine for me for now.

So, in short - There's absolutely no need for a smart trainer if you have a decent dumb trainer supported by Zwift, or if you have a power meter. Virtual power from some trainers, especially magnetic resistance types is not as good and I wouldn't enjoy it on those.

P.S. The best dumb trainers to use are those that are supported by "zPower" including the Road Machine as I mentioned. As I understand it and if I remember correctly, this is basically a more refined version of basic power curve approach which also includes rate of change of speed rather than just a steady state power to speed relationship. That makes it more responsive and realistic when changing power/speed for sprints, intervals, etc....

P.P.S. If using a dumb trainer, use the same tyre pressure and clamping pressure each time to ensure the power curve matching is consistent from one session to the next. Doing this, mine seems very consistent.

If you've a half decent dumb trainer already, try it with that first. You should get a decent idea whether you'll enjoy it. There's a free trial and the subscription is monthly and modest so there's no real risk there. Try and if you don;t like it, cancel.
I started with a dumb trainer and would have been willing to upgrade to a smart trainer later if I thought it would be significantly better but I've been happy as I am. See my comments in the post above.

If you don't have a trainer at all and you're not sure if you want to invest several hundred on a good new smart trainer, why not buy a second hand dumb one to try it out. I'm pretty sure lots of people are getting rid of theirs! If you're confident you'll use it, get a good fluid trainer or a decent smart one. IMO the quality of the trainer does have an impact on enjoyment but smart or dumb is less of a factor for me.