I don't think the exercise part of decluttering has been particularly helpful to me, but I've definitely enjoyed the benefits of living in a cleaner environment. For one thing, it is a lot less tempting to grab a junk food snack from the cabinet when the kitchen is clean enough to enjoy cooking something. I've also tidied one of the bathrooms quite a bit and the rather nasty roach problem (hey, it's an apartment and the walls are probably infested) has all but disappeared.
To elaborate: I'm not a nasty person with a certified biohazard tub area or anything, but changing the shower curtain and removing some extra items that provided cover has caused the little buggers to steer entirely clear of the bathroom area, it seems. We previously had a roach problem no matter how many times I wiped down the sink, counter and shower because they could sneak along the perimeter and reach the tub for the resource they wanted, water.