This is the case if content with file attachments is deleted normally.
For whatever other reason if there are files (attachments etc) not related to current content as I have with files leftovers from the upgrade from 3.x to 4.x me /uploads folder ended up almost double-sized (I think something went wrong with the upgrade back then). That is a big problem as the folder is 12G and the duplicates are almost 4G from 3.x since then. So there is an issue with this.
There is a need for a tool that will locate unused files (not registered in current IPB db as content attachments) in /uploads folders and either delete them or at least move them to a temp location for further investigation, cleaning up /uploads from redundant files.