PS Tracker monitors disk space. It helps you to be aware of your profile size and thus your hard drive usage. Nowadays, we run out of space easily while working on different projects or synchronizing our mobile device(s); not to mention faster but smaller SSD drives. Avoid unexpected crashes and freezes, as hard drive gets almost full.
The menu bar's icon
Note: Your Mac needs adequate hard drive space to operate normally. A low amount of RAM requires more drive space for Virtual Memory's swap files.