I've had a few characters I've reused, mostly due to a lack of use in an RP or I wanted to explore them in a new light. Typically they're a character with a unique perk or style and I already know the direction I can take them. It also means I can refine an idea that I may not have been happy with at the very beginning.

In saying that, I still will have the one offs that I won't revamp. Some characters are just too difficult to place them in a new setting and by the time you do the only similar part is the name. At which point I would look for a new name as I often associate the name with the style of character.