This is quite a common thing but a lot of people are also completely opposed to it. Do you reuse your RP characters in different RPs later on? Why/why not? Do you have certain rules about what they can be used for if you do?

Unless it's a sequel to another RP, never. Crafting an original character for an RP is the least I can do for how much work many people put into making RPs.

Ah, re-using a character for an RP. While I may only be in one RP here, I used to do some roleplaying on this other site long ago. I'll be honest, I did re-use a character, but it was a "sequel" roleplay so that worked, but looking back, I feel like I was kind of cheating at making characters. I essentially just took a character from a game and added personality traits that I liked. So, really, just try and make something new, you'll probably like it much more and it would be more fun for you and others! Just don't be obsessive like I used to be.

All the time. I just reskin them, shuffle their attributes around a bit, modify their talents and history to fit the world, and adjust personality to match my current mood.

Oh, wait, that's just making a new character.

I don't think I've ever reused a character per se. Sometimes I come up with an idea for a character or power for a RP in my brainstorming process, but never end up joining or using the idea. I've used the idea then in other RPs - Sophia from Gunpowder is a really good example, her powers were original but her personality, name and faceclaim were meant for another RP which I never joined.

Absolutely.
More often than not, this takes the form of taking one of my existing Pokémon characters and placing their profile in a forum SU.
You see, I have a collection of Pokemon characters that I'm very passionate about, but who have only seen the 1-on-1 kind of RP, never the group RP variety.

In one case, I have a character who I have taken from group-RP to group-RP even within PokeCommunity: my Xatu.

In some cases, I make entirely new characters. But whenever I've tried that, the GM has to disappears after a few posts, and then I end up adapting that character I made into the aforementioned list of characters for 1-on-1 RPs, since I can't play it in "group" anymore.

I never used the same exact character, I try to change it up, but they always tend to be similar. For example, I usually RP as characters that are good, I have tried being a bad character before, and I just can't do it.

So I don't use the same character, but they always tend to be similar. Besides, most rps I enter usually don't end or get very far, so I tend to grab ideas from those characters because I was never actually able to finish with that character.

Absolutely! My characters begin as archetypes with certain quirks and a team of pokemon. Their history / bio is always the last thing I do, and so re-using them is quite easy since that's the only thing that 100% almost always needs changing. It'd be a waste not to reuse the character base if the opportunity presents itself.

I haven't had enough opportunities to reuse any of my characters yet.

I wanna say I've only reused a character once (maybe twice but the rp never actually started), but i only did it because i felt those characters fit the rp really well (with slight alterations), otherwise, i create new characters because I've really grown to love character creation