I'm getting TM backups whose sizes don't match the target. My 260GB content on MBA SSD may produce a 220GB backup. My ~125GB IPhoto lib may produce a 95GB backup. Yet the other 30GBs of photos in the pictures folder back up to precisely the same size as on the SSD.
I've read TM does no compression. and I've had a tech support guy tell me that much difference (~25%) in the iPhoto lib is normal. But he hasnt explained why the size of the other pix (or music or movies, for that matter) isn't reduced. I'm left worrying My iPhoto lib isn't being backed up properly.