The only reason I've ever wanted a dedicated bike head unit is for Varia RADAR support. I don't have the RADAR, but I want one....and the 920XT doesn't give you the graphical rear SA picture like the head units do. I could get a dedicated Varia head unit, but that seems wasteful also....so, I still have nothing.

Other than that, I'm a watch only guy.

Another use case might be to have bike specific (power, cadence, etc) data diaplayed on the head unit, and "other" data on the watch.

I bought my Elemnt after I got lost on a ride away from my usual stomping grounds. The stress caused by my fast draining phone battery made me decide to get something I could load a route on, that would give me cues, and that could re-route when necessary.

When I started using it I found out that the improved ergonomics (buttons you can actually press when riding, displays you can read) are nice as well.

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Citizen of the world, former drunkard. Resident Traumatic Brain Injury advocate.

I use an older Garmin edge.

1) While riding i can instantly see stuff like cadence, speed, distance, heart rate, whatever without having to move my hands.
2) I live in a densely populated area with a lot of traffic and with the garmin i can see crossings and stuff like that ahead on the map, even when i'm at the back of the bunch during group rides.
3) When i'm travelling i use it as a navigation tool. I install maps of the country i'm in and plan a couple routes ahead of time. That way i don't have to mind where i'm going that much and i won't get lost.

You can live without one i guess. I allready had one before i got the watch. Still use it though because of the reasons i mentioned.