I get locaps when i can afford them. (Having just switched from an M4, with which I had 10 locaps to an AK, I currently only could afford a highcap.)
couple of reasons:
2)Ammo concious, i worry more about making my shots count, and know when it's time to fall back and reload.
4) If i need to, I can get a couple shots off lying down (my gun is sideways), doesn't always work with high caps
5) Reliability - they don't randomely unwind on me, and are more consistent.