I think you just have to listen for what is called for in a particular song, band, style, etc., and also be conscious of what your body is telling you. I used to play nothing but hard rock, and I still love the sound of really digging in finger-style when I play the heavier stuff. (I still play in a couple of groups where a heavy style is what's called for.) These days, however, I play a wider variety of styles, so I've learned to back off when appropriate to the song, which gives my hands a little rest. I'd say just don't box yourself in to any one way of playing, use your ears, and be aware of any fatigue you may be experiencing, as this could lead to injury.
Also, I read a Billy Sheehan interview when I was a kid, and he talked some about the athletic component to playing. He recommended stretching and warming up a little before playing, as well as stretching after a gig or rehearsal, just like athletes do. I've found this to be helpful in any sort of repetitive motion scenario with my hands--playing bass, typing, wood working, etc. After 20-plus years of playing fairly aggressively, I'm happy to report no permanent aches, pains, or injuries to my hands or wrists or the muscles, tendons and whatnot associated with my playing. Even when playing upright bass, which I find to be far more physically demanding than playing electric, I've been able to maintain my overall hand "health," so to speak.
So, in short, two points: Play for the song, and be aware of your body's needs.