If they are in a post-Eternal-September situation, they follow the Facebook.com path: grow at all costs, then coast and squeeze revenue until the last wave of users leave. (FB's TAM is "everyone", so it's lucrative. Most others have a smaller market).

If they are in a pre-Eternal-September situation and they want to avoid Eternal September, that's different. Then, they should work to slow user growth, improve onboarding, and have some moderation. The goal is to integrate new users slowly, so they buy into the culture before they change it. It's difficult.