Skittles has cuttlebones in each of his cages but he doesn't use them much. He has a cement perch thats part of one of his playstands and he uses that to file his beaks. Particularly with conures, since chewing is such a common trait, I think having well groomed beaks is very important. I don't think they are necessarily trying to 'sharpen' them, but rather are trying to groom them to keep them in proper shape. I've seen a lot of sunnies with 'flaking' beaks and my vet says that is normal (they chafe off), but by providing things like cement perches or cuttlebones, the flaking can be minimized. Skittles is very good at 'self-maintenance'. Its like he knows how cute he is and insists on keeping up his appearance. I try to keep his beak as free from flaking as I can. I don't like how it looks and I worry about bacteria growing in the crevaces since he also eats fresh fruit and veggies and sometimes I do give him baked or broiled chicken as well as hardboiled eggs.
You do want to be mindful of overgrown beaks. They can be deadly because they prevent the bird from getting enough food/water.