Just discovered this.
I usually take all my photo's at full resolution (6-10mp)
This does however eat into HD space.
For my non family / non essential JPG's, previously I would use Graphics Convertor to reduce file size to around 200k, much better then the original ≈ 2mb per jPG.
I've just discovered a really useful option in Preview, that is to "Save As" (JPG) whereby you can select lower resolution, which in most of my JPG's reduces file size from 2mp to around 100k, quick & easy.
Retains quality quite well too.
I also use Preview for non PS7 cropping. Nice option.