Personally? Never.
(I know...I'm a chicken. I cut one into the quick one time and I was done) I do take him to the groomer probably 3 times every 2 months to have his nails dremeled. He does not get to walk on concrete very often, except for in our basement, and his nails grow like weeds! I like them kept fairly short, so I happily pay someone to do it, and I have his feet clipped at the same time.