Disk Quotas

Each user user's home directory is limited to a certain size. The default size is 1G.

Filled Quotas
When a disk quota is nearly full, it will become difficult to use the computer. Web browsers and any other applications that create a caches will encounter problems.

Freeing Space
for i in `ls -al ~ | awk '{print $9}' | grep -vE "^.$" | grep -vE "^..$" | grep -v 'yesterday'`; do du -s $i; done | sort -r -n | head -n 15

Will list the 15 largest files and folders in a directory.

Web browsers often create large folders for bookmarks and cache files, which can be deleted if the user doesn't use the web browser in question.