I first truly had the need for recovery pace when I began commuting by bike and realized I could suddenly add 5+ hours of training per week without sacrificing work or family time. Like many cyclists might do I simply couldn't believe my luck at having the opportunity of doing that many more miles.
But adding that much workload is not good for going fast. I ended up getting a little run down for a while, and tried going slow to do a recovery pace, but had trouble embracing the truly slow. When you've been doing nothing but going fast for years, it feels like a big shift.
Eventually, though, I figured it out. It's simply so slow that you never feel like you're putting effort into the pedals. That said, you should always be pedaling, always spinning. Because the power into the pedals is so low, even the smallest climb will slow me down to about 5-8mph. It felt foolish at first (I can go SO much faster than this!) but after doing it enough you can feel the benefits and that makes it easier to embrace the pace.
It's essentially the equivalent of walking vs. running. It's a completely different pace.
EASY WAY TO MAKE SURE YOU'RE DOING RECOVERY PACE:
The pace should never get high enough that you need to breathe through your mouth.
I prefer on-bike recovery to simply taking the day off because my legs don't stiffen up as much and feel a bit sharper after they're rested. When I take days off I usually have to do a spin to get the muscles limbered up again, and then the next day they're ready to go again. So I can do 3 days of active recovery before a race, or take two days off and do openers the day before. If I'm doing active recovery, I don't need to do openers.
Sometimes you just have to take some time off the bike. Even recovery pace has it's limits, I believe, and I do take days off. Often around races, but sometimes I'll take advantage of traveling or vacation to take some time off. Unless of course I can bring my bike.