LR backing up

when I start Lr and there is a window that pops up asking me if I want Lr to perform a back up, What exactly is it backing up?

i am assuming it's just the info on imported images, locations and edits to photos.

Thumbnails / previews, etc etc.
My backups are getting humongous though. Already 10gb space on my C drive. Not sure how to handle this. I deleted some old backups, I guess I could tell it to delete old previews after a while, but that means extra time waiting when I decide to re-process old photos or take a second look at them.

It is backing up the database. All of the settings used in LR are stored in your database. You can set LR to backup daily/weekly/monthly by going to Edit > Preferences.

As far as previews go LR tosses them out after 30 days by default so don't worry about the space used for them.

Grab a cheap external disk or two and use Synctoy to make copies every few weeks. Keep the drive powered off between backups. =)

In2Photos wrote in post #3095104
As far as previews go LR tosses them out after 30 days by default so don't worry about the space used for them.

I believe that's only true for the 1:1 previews, not the standard size ones. If you tossed them all you wouldn't have any for the images you store offline.