There can be any number of reasons to do this. First of all, while a passion can be a stimulating thing, it can also be draining if it’s your only outlet. One of the surest ways I’ve found to break a block is by getting the heck away from what’s got you blocked, even if only for a little bit. If you’re a photographer, this might mean taking some time to write, cook, sing (well or badly, it makes no difference) or do any number of other things. One of the surest ways to get something done, to paraphrase Robert Benchley, is to pretend you’re supposed to be doing something else (I once cured a case of writers’ block by convincing myself I was supposed to be learning Spanish, for instance).
Second, your photography doesn’t — or shouldn’t — exist in a vacuum. Inspiration isn’t purely a visual thing, even when you’re working primarily in a visual medium. After all, think of how many visuals work because they’re not purely self-referential. They draw on cues taken from design, music, literature, sculpture, or any number of other media. Being grounded in other disciplines and interests means never having a shortage of inspirations or subject matter.
Finally, it’s not just for your own sanity, but also for the sake of the others in your life as well. If you’re lucky, your friends, family, spouse, et. al., understand how important photography is to you. However, if your every conversation circles back to technique and gear, people will get tired of it — and perhaps, of you — pretty quickly.
So. What about you? What other interests have you cultivated, and how have they intersected with your photography?