JFFS2 compresses?

Does JFFS2 compress data in flash?

When I check the available space in Flash

df

Filesystem 1k-blocks Used Available Use%
Mounted on
/dev/mtdblock1 32000 5772 26228 18% /

But when I erase a file that is 702k big I get:

df

Filesystem 1k-blocks Used Available Use%
Mounted on
/dev/mtdblock1 32000 5648 26352 18% /

Which means that 124k have been freed.
I think there is a compression algorythm involved...?

Thanks a lot