I've always had a pretty hard stance against the concept of just tweaking one character, over and over, for multiple RPs. It's like the Ash Ketchum of RPing; Ash isn't an interesting character because he can't ever grow because of the status quo. Keeping with one thing for too long is just adding water to wine, you dilute the experience to the point of meaningless. I personally don't even see the appeal of keeping with one character unless you're self-inserting, which... is interesting.

Making a different character for each RP you join also just leads to more interesting characters, as far as I'm concerned. It gets you to write multiple personalities or make something that slots nicely into the cast instead of having overlap with others.

The only time I'd personally re-use characters are in reboots or sequels. A reboot leads me to get a second shot at writing the same person, maybe with some tweaks to their base to make them more interesting from the get-go and take it in a direction I couldn't before. As for a sequel, I'd only use a legacy character as a side-role at best, as they've already had their time in the sun and I don't want them to be an Ash.

No hate on people who stick to one character, tho. You do you and you have fun; it's just never something I've agreed with. Even in my Tumblr RPing days,[i][sub](shudder)[/sub][/i] my one character was continually built on instead of having a soft reset each time. It helps I made him a dimension traveller back in the day, but I didn't want to take away anything from them each time I started a new RP.