Disk Space not increasing after deleting large files is probably due to Snapshots!

Macs now save a "snapshot" of your startup drive automatically if you use Time Machine. Typically they only last 24 hours with TM, but sometimes they just sit there seeming to take up space (they won't if you need it, but it still looks like you have a lot less free space than you really do, which can be scary). TechTool Pro also saves snapshots (in the same system data space as Apple does), for 4 days (dep. on preferences). Nice for recovery but not seeing that freed up space on the volume icon on the desktop, or in Storage in System Settings (many TBs taken by System Data from my 8TB startup internal SSD) is disconcerting to say the least. Also TechTool Pro monitor will warn you with a pop-up of not enough free space dep. on your settings. That's also scary. If one knows there's no problems with their precious data, it seems rather safe and satisfying to do the following: Go to Disk Util, Choose View at top menu, choose view snapshots, select your old snapshots and hit the "-" symbol to delete. My "free space" went from 800GB (less than 15%) to 2.5TB instantly. Whether or not it actually "frees" the space, it's nice to see it right there on the desktop for most of us. After checking this obscure topic online and then going into TechTool Pro Monitor, apparently TTP was set to do a snapshot EVERY HOUR by default. Each snapshot was about 60gb. There were over 70 with the filename TTP, with only a few named Time Machine. After days of research and an Apple Support ticket, I finally figured this out and am back up and running fine. Snapshots should be far more up front and center within the Storage section of System Settings in my view.