There is a limit to the amount of storage we have for files we upload using Google sites. With Google sites, you can create a "File Cabinet" page type to hold files you upload, up to 20MB in size for each file.
According to this page, our domain (blakeschool.org) has a limit of 100GB of file space. Whereas this equates to 5000 files, once this space is occupied, it is gone.
There is no limit to what one user (including faculty, staff, administrators, and students) occupies, it is common space, and thus incumbent on any one user to clean-up their files from time to time once the purpose of your post is past it's useful life.