Does editing compress my JPG:s?

["Antti Ahonen" <aahonen gmail com>]

I like to use these editing features of F-spot for all simple editing
I do, like cropping and minor color adjustments. Only now I noticed
that the size of an exported jpg is much smaller tahn the original.

If I have 2.8MB JPG, after editing (any editing, no cropping) I will
have about 600 KB image.

So what have been lost?

And why is the size of the file not visible in F-spot?