Photoshop uses a lot of RAM. It will take as much as you can throw its way, and then some more. As a way to use ‘more’ RAM than a computer had available physically, the developers took to creating scratch disks on your Hard Disk Drive (HDD), as an extension of the data that Photoshop held in RAM.
If you don’t do this one thing, you will lose all your edits when your lightroom catalog file gets corrupted.
This is the one setting that I always turn on as soon as I install Adobe Photoshop Lightroom (LR) on any computer: Automatically Write Changes into XMP.
I suggest you do the same, because it has saved me many times. I really don’t know why Adobe sets this to ‘off’ by default. It should always be turned on! Here’s how to turn on