Free Space Note

I’ve known that our macs delete sometimes GB of data at startup from their /tmp directory, but I didn’t know it was possible at a log-out; log-in basis. Just now when installing a helpful Spotlight enhancer I had to log-out and back in to activate the plugin. Before I logged out I had 30.05 GB remaining and now I have 33.16 GB remaining. Have any of you noticed this? Does anyone have any idea of where the data is that gets removed?