periodization, on the physical side works, if you;re already at a high level realtive to what your body and genetics allow. If you're just another avg rider, not terribly fit, not terribly strong, not riding big miles - it means hardly nuttin.
Psychologically however, it means a bunch. It's the rare bird that can go hard for long periods and not have a letdown - Merckx being a top example of this bird. One sees the 'letdown' often in Pro sports, especially those with long, hard seasons, like Hockey, B-Ball and cycling. Most of us just can;t keep that focus and bring the energy to EVERY competition for months on end; so some sort of diversion helps. I like skiing, and add some surfing in winter (when we actually get the best/largest swells) recently back playin hockey - all makes a good mix.
But I still do hard days in the bike in winter, and make the easy days for sure easy. I climb a little less, suck wheel a little more, splash around in the mud on my MTB on those infrequent wet days we have...
Burnout can happen, without your intent, so pay attention to the signs and it's easier to take an easy day in the off-season than later on... Otherwise, if there's chances for big gains to be made, don't get to an obvious backslide.