so i will give you some of my tips and i hope it helps.
to start I'm a daily/habitual user of CM, i use portable version on my USB at both home and work, home i do light work and most of what i save i want to save permanently.
for this i create my folder structure, once the folder is created right click it and choose properties, now i don't want CM to clean out this folder so i set purging rules to never, and at the bottom i don't allow it to catch new clips.
i choose to do it this way so i manually have to drag the clips i want stored out of my inbox and place them where they need to be..
now at work it varies more on the temp/useless info..
i do the same method for storing the stuff i wanna keep
for stuff i don't... now because of the amount of clips i take in in a days time which is well over 1-2k
I set my purging rules by number of clips, i used to use by x days but my database easily hit 500mb daily
now if you run up a lot of erroneous crap like i do you will also want to set purging options on your overflow folder.
now per the help file "The cleanup usually runs at start up, shutdown, or it may do a little bit during long periods of idle time."
and i do have down time at lunch and of course it cleans up when i start and close for the day so for an 8 hour shift this is good, i typically don't leave my USB in any 1 place longer than this unless i am working on a project of sorts but you can manually clean this up by going to file > database maintenance.
hope this helps some with what you need.