I assume you're using smcFanControl or similar to keep the idle temperatures lower. The fans will at some point stop spinning anyway, and keeping them running a slight bit faster at all times will surely shorten their lifespan a little. How much in real terms? I don't know, probably not long enough for the rest of your MacBook Pro to keep up (read: you likely have a new computer by then).
But it is not needed to bump the fans up a notch anyway. The SMC controller should take care of that on its own. The only benefit is that your MacBook Pro will run a bit cooler, making it more comfortable to use on your lap. If that's your intended use however, put something under your MacBook Pro like a small pillow and you'll barely notice the heat anymore. And you'll have a quieter computer to work with.
Let me know if there's anything else!