Should really only be done if over grown. Yours don't look too long to me. Feeding on a piece if slate, having rocks to climb over, etc, will have keep them the length they should be.
Also, I believe they have blood vessels in them after a certain point, unlike human nails, so you need to be really careful in case a little trim suddenly becomes very spectacular and painful. By the way, the nails in your picture look normal to me . I'm sure the RTs are very proud of their long nails, and they certainly use them a lot when they're climbing around. I agree they'd not be great if tortoises were giving massages though, but luckily they realize that too and don't usually try it.
I have had animals all my life and have had experience finding the blood vesicles in nails. I clip my torts nails occasionally, only if they are really sharp (sometimes she claws up my hands with them). I am not sure if this is the case for reptiles, but if the nails continue to grow long with no maintenance, the vesicles can grow with them (this happened with my guinea pig when she did not allow us to clip her nails so she had to get the specially clipped). Just look for the little line inside the nail when you do it and you'll be fine