A relevant comment on this issue was posted by user @teres3 on another thread:
https://forum.torproject.org/t/new-release-tor-browser-14-5-4/19562/5
The user’s point re Cloudflare is a good example of a use case where previously changing security level mid-session (from “Safest”) was useful.
For instance, when you would temporarily downgrade to Safer in the past, was this workaround exclusively to enable JavaScript on a temporarily basis? Or are there other reasons you would downgrade mid-session too?
Enabling JS (for turnstiles/captchas/other required functionality which is broken in “Safest”) on a per-site basis is what I am primarily thinking of.