My hard drive magically gained space after erase and restore... how??

So my iMac was crashing and it wouldn't start up. I tried booting from a disk and all that jazz, and Disk Utility said that it couldn't repair the disk, so I erased and restored from a Time Machine backup. Before this all happened, I had around 40GB free. Now, I have 114GB free! I can't tell what's missing, so I'm not complaining, gaining 70 odd GB without trying is always a good thing, but I'm baffled as to where this much free space could have come from!! Any ideas? Thanks guys

Probably lots of cache files and temp files left over from crashed apps that had been hogging up all that space.

Also any swap memory files would have gone on on a fresh system