Video takes up a lot of hard drive space. HD video more so than SD, 4K more than HD... and since the flooding in Thailand, hard drive prices have spiked precipitously. So there's always room in an editor's toolkit for an app to analyze drive space and zero in on the largest directories to delete or move. Similar to my approach to tracking time, freeing up space is all about focusing on what's important: in this case, the largest files. DaisyDisk is a paid Mac app that I find myself using frequently; here's a review from NextUpMac (and a free alternative).
Video is no longer available: www.youtube.com/watch?v=kdXREP82Uuo
Normally $20, DaisyDisk has been $10 for quite some time. The visual interface really works, in my experience: it's not just for show. However, if you think $10 is too much to pay, check out a free alternative on the Mac: OmniDiskSweeper. Windows users, any suggestions for managing disk space?