I keep atleast one in every enclosure I have. The way I look at it is, they are very cheap, will last if not eaten right away, allow the tortoise another source of calcium if and when they decide they want more, they are good for the beaks, and are simple, easy, no fuss things to give them. For me, it's a win win, even for those animals who never seem to touch their cuttlebones.
Good comments above. Yes, each of my tortoises has a cuttlebone in his/her pen. The female uses it, nibbling on it from time to time, the male doesn't now, but at some point he might. Cuttlebones are a good source of calcium, and keep the tortoise's beak trim. They are also cheap and easy to use; just place them in the pen and let the tortoise do with it what it will. No reason not to use them.
funny you should ask this, because when I moved my RF's outside, I just put big pieces of the cuttlebone in various locations of the enclosure. I had been just sprinkling the poweder or relying on their greens. It was amazing, all of them at some point found a piece of the cuttlebone and began chomping on it. That tells me, that they were needing it or just curious. Either way, I am leaving it in. Now if I can just pick out all of the little rocks that keep popping up as they walk about, I will really happy.