Why does my %appdata%\Local\Temp folder have almost 100GB in it? If this data is disposable, why hasn't Windows told me?

Question

Hard disk failed. With a little trickery, I was able to coerce the Windows Backup and Restore 320GB VHD drive partition image (which contained only 220GB of actual data) to restore it onto a smaller 256GB (actual ~238GB) partition on my new SSD.

After going through the expected repair, since the drive layout changed, everything is back up and running fine, and all that's left is to update my special folder locations (I used to have pictures, desktop, video, etc. folders on a separate data partition). While doing this, I noticed that almost HALF THE DATA ON THE DRIVE (~100GB) was in %appdata%\Local\Temp.

Is this safe to erase? Why would a temp folder end up with so much data? Is that where things like WinRAR store decompressed files temporarily?

I'm asking these questions, because I'm just very surprised that all this time, it looks like half the data on my main OS drive was disposable, and Windows never clued me in on this. With only 238GB on my SSD, 100GB is precious space.

Answer 1

Yes, in %APPDATA%\Local\Temp or %temp% for short it is safe to delete files. Files that are in use and important for programs will be locked (i.e. open).

Windows does not delete files from this directory itself however if you choose "Disk cleanup" in the properties of the drive it will include a clean up of these files. (Make sure to never click "compress old files" in that dialog.)

You can also use a program like CCleaner to do regularly cleanups of this area. I use it instead of "Empty Recyclebin".