With a light running schedule, say only 2 or 3 days a week, you probably don't need any recovery runs. But don't feel obligated to make them all hard either. Run hard when your body feels like it but if a run day comes up and you are feeling beat, you aren't going to be doing yourself any favors by forcing yourself to run hard. In other words, when a run day comes and you need recovery either don't run at all or do a recovery run.

When you are running frequently, you definitely need recovery days. Many of them.

I'm guessing you want to make big bike improvements. If so I'd recommend only doing easy runs so that you can hammer the hard bike workouts. Maybe do a couple of miles at tempo per week max.

When you say that the recovery runs "helped", do you mean that your experiments indicated that the fastest way to recover from a hard run/ride was a short moderate pace run?

I would argue that if Hal's "recovery runs" are accurately named, than this is really a conversation about recovery. So, first you have to decide whether or not Hal's recovery runs really did make you recover faster, or if your recovery was more a matter of "despite" the short, moderately paced run. The reason I'm obsessing over this point is that "Moderate pace" seems a little fast for a recovery run.

Once the above gets figured out, carefully monitor how fresh your legs feel the day after hard workouts. This can actually be kinda tricky. I use the ease of walking up a couple flights of stairs as my measuring stick. When you need some more recovery and if you've decided that short moderately paced runs do speed recovery, then do them. If they don't speed recovery, trying doing them dog-slow and see if that aids recovery.

Let your recovery requirements drive the show. If recovery doesn't seem like a problem, experiment with making the workouts harder or longer. If you've got no zing in your legs when you're trying to do an up-tempo run, than you're not recovering enough. Recovery is worth obsessing over.

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You may not need them, but running more often is helpful.

Why not add a 15 minute easy run after an intense bike workout, as a form of cool down.

When I have an opportunity in my schedule I ride an easy warm up then time my intervals so I a end my ride once the last rest period is finished. Then I go out for a quick run at an easy pace (I.e. Zone 1 or 2). I just focus on form and turnover.