Some users experienced accidential growth of /var/log. Some users experienced accidential growth of /var/cache. Some users experienced accidential growth of /var/lib. Some users experienced accidential growth of ~/.xsession-errors. Shall I continue?
Does every user need to begin his day checking all that places? No, he does not. It is waste of time. Such situations are extremely rare. If you are paranoid, check df to see if you have enough free space, and only if it unpredictably shrinked begin to ivestigate which directory has grown.