1. The samples are 12gb because there are multiple velocity layers - great for real drums, not the best when you have to hunt through them to line 'em up like my man Tarekith does.
2. Impulse, Simpler, Racks, and Sampler render the need for Battery to a lower level. Again, great for real drums, but for an electronic music producer, not a big benefit.
3. CPU usage is good, but make sure you set the default outputs in the prefs to what you need. The default is 8 Stereo, 8 Mono, which uses up a lot of CPU right out of the gate. Also, a lot of the kits use per-pad effects, so they can tend to eat up CPU.
On the flip side:
1. Ease of use
2. Stability
3. Insta-drums
4. Lots of presets
5. Quality sounds
Since you've already ordered it, you might also look at Synthetic Drums I & II for Battery.
Ok, I'll now get ready for the flames comin' my way