Simply without going into the details of the previous posts (but they are correct for those willing to take the time)

Macros make your abilities have a delay rather than go when the GCD reaches 0.
Bigger delay between abilities = lower DPS.

Also if you queue whole Combos you can only do second wait times so you will either do your skills 3 seconds apart which is MUCH slower, or have the macro try to do a skill after 2 seconds and therefore miss the middle skill of your combo out.

That didn't end up being much shorter did it. Oops.