I have a fairly extensive list of characters. However, I am quite strict on how they're shoved into settings.

Most of the time it is simply convenient to create a new one for the almost inevitable temporary nature of a thread. When the thread dies, the character joins my canon, and thus becomes persistent in the background.

Occasionally, a roleplay may fit one of those characters, and said persistent character is brought into the roleplay. If the roleplay goes well enough, the events are canon to the character, up to and including their death. If the roleplay is poor or the development is stunted, I ignore the results entirely and keep the character on the backend with no changes other than a few 'well that was weird' tweaks.

The characters made anew are a mold, which I usually end up using beyond their proof of concept stage. Once they are used beyond their intro, they become persistent, and every roleplay/backend lore experience becomes a permanent addition to the character.