Why does the space become smaller?

I was trying to clean out my laptop,but after that, my space just kept getting smaller! Before i started i had 1 point...something i can't remember, and when I stopped I had 311 MB then I checked again and i didn't do anything but it went up to 806 MB and now it is 799 MB and i still haven't done anything. Whan happens?

Were you using win zip or win rar,if you interrupt during compression it would take up space.

Download CCLEANER and run it to clear all junk and useless files.
If you are using win xp,click START and click RUN,type %TEMP% and hit enter,delete all the files in that folder,some files may not get deleted,just ignore those and delete the rest of them.
If you are using win 7,click START and type %TEMP% In the search box.

It must be a bug.