group.cacheAsBitmap performance

[ForgeableSum]

I've often tried to use cacheAsBitmap on a complex group (say one with hundreds of non-moving, static sprites) and am surprised to find no impact on performance. It clearly works because if i try to move a sprite in a group with cacheAsBitmap on, the sprite won't move (because the group is cached). What I don't understand though is the performance benefits. I've literally tested this in dozens of scenarios. Has anyone find an scenario in which cacheAsBitmap actually improves performance? 

[tokumaru]

I used this to cache the walls in a dynamically generated maze (about 150 sprites) and the performance improvement was noticeable, specially on my phone.