When we first got the two cats, the shelter recommended clipping them every two weeks. I tried with Swanie - a rather large male tuxedo cat - and two of us couldn't hold him to do it. He really freaked when he saw the little cutters they sold us, and I think that's why he stopped getting on my lap. Before I tried that on him, he was on me as soon as I sat down.
So.. I went searching for the reason to clip a cats claws. According to just about everything I've seen, the main reason is to keep them from scratching your furniture or scratching you. I even talked to the vet because I wanted to make sure it wasn't something that would be hurting the cats if I didn't do it.
So, I've provided them with a ton of scratching alternatives to my furniture (and if they do scratch it once in awhile - oh well - the price I'm willing to play for having two beautiful cats live with me.) And other than the first month or so until I learned the right way to play with a young male cat with lightning fast reflexes, I haven't been scratched by either cat. Even when I've had to give medicine or put drops in eyes.
I do watch, and if they ever look like they're getting curled or seem uncomfortable for the cats, I'll take them to the vet.