Running out of hard drive space is incredibly annoying. OS X needs a good amount of free space to function properly so as things get full not only will you be unable to download or transfer large files, you'll start to get panicked warnings from the operating system. While hard drives keep getting bigger and cheaper, solid state drives do not. If you have a 2TB HD in your machine you'll be okay for longer. If you have a 128, 256, or even 512GB SSD, however, things can get full and fast. So what do you do? If you can't or simply don't want to upgrade your HD or SSD drive to something bigger, the first step is identifying what's causing the problem, then figuring out what you get rid of to free back up that precious empty space!