TL;DR of the post and its discussion, generated automatically.

Roblox says that from November 11 the server auto-destroys old Player and Character instances to stop memory leaks. Opting out ends in late February.

• Forced switch: questioned making it mandatory, then called it a pretty reasonable update.
• Why not: no real reason to resist forcing it, unless you like memory leaks.
• Client side? asks when the same behavior comes to the client; no answer yet.