The general admonition against using macros for combat is because the typical question (or the typical question that I see, anyway) is, "how do I macro <some GCD-based combo>?" Here's an example hot off the presses, in fact. There are cases where macros can work in combat, as even The Balance will attest to.

But really, none of that has anything to do with increasing the number of macro slots available. I have a whopping 14 defined, and it will cause me no harm if I suddenly have twice or thrice as many slots to use. Have fun with 'em.