Gained files/data upon deletion

[BestGuy]

I had not run CCleaner in a long time, many months or maybe even a year, was hoping to run it and save some space.  I Analyzed first which found that over 5 GB of data could be deleted, like 5.72 or 5.79 GB of data which I thought was great, better than I expected.  But this is how things started to get weird.

Just by running the Analyze: my Total Available disk space went up from 66.something to over 677.something GB, and then once I actually ran the Cleaner it only went up to 70.3 so why did it say over 5 GB was going to be deleted when it only actually deleted maybe over 3 GB in reality?

[CSGalloway]

Following

[nukecad]

There are a number of reasons why what CCleaner estimates can be cleared differs from what actually gets cleared, and you have to remember that what the Analyze/Scan comes up with is only an estimate of what can be cleared.

Those reasons could include things like:
Files that would normally be cleared but are still in use so can't be deleted, eg. files that weren't in use whan you Analyze that have started being used again.
Windows files of a fixed size that CCleaner deletes to clear the contents, and Windows puts straight back as empty files of the same size.
Synced files that CCleaner does delete, but get immediately synced back from the cloud. eg, synced Browser data and history.
Files that Windows had listed as being there, but which actually didn't exist. eg. the corrupted Recycle bin issue.
There are other possible reasons.
See the link in my signature below this post - the section "Files that re-appear straight after cleaning:"  gives an explanation of what may be going on and how you can stop some of it.

If you want to try and track down just what those files are then you have to use Custom Clean to see what an Analyze is finding (File list in Advance settings, or double click an category after the Analyze), Run Cleaner, and then Analyze again and/or check in File Explorer to see if they are still there/came back.
That's a long job to check everything, and TBH isn't of much practical use anyway..

I long since stopped bothering about differences between what Analyze/Scan says and what actually gets cleaned.
Lets face it, with the large capacity drives that everyone has these days if you are scrabbling about to save a couple of GB space then you have bigger problems.
It's not like 15 years ago where an average laptop would have a drive of 32GB capacity or even smaller, average drive capacity is much larger these days.
If you are struggling for a couple of GB free space then get and fit a larger drive, you can pick up a top named 500GB or even 1TB SSD for relative pennies these days.