I often create very long compositions (like 10k frames) to make sure they can easily be reused anywhere without having to change their duration if they're too short.
Problem is: If I don't set the work area to a shorter duration OR forget to deactivate "Cache frames when idle", Ae fills up all the system RAM. That's not a big issue if it's the active comp, because each change in the comp will empty the cache, but when switching to another comp, all this cache will be kept, and the system just becomes unusable. And then I'm angry because I have to go back to the longer comp to disable "Cache frames when idle", then empty the cache, then get back to work. And I don't like being angry 😉
A simple change would make be very happy: in the preferences, add an option to limit the duration of the cache when idle; for example, it would be nice to be able to set it to "cache around current time" AND no more than 1s before and 5s after, for example. That would prevent this kind of issue, while still being quite useful.