When the game was live I use to use macros extensively and I am re-remembering things. I would use them early on for costume changes. My fire tank would come down with an area attack and change all at the same time, or a super speed spin power and change. Later that became more common place.
I would also make a complicated series of macros that that with certain slots would be a macro, it will same something local often to the selected $target, execute the power, change power trays with an identical set up that would have one macro set to do something similar just with some other thing it says then moves on to another tray of duplicate powers etc.
Other obvious uses was things like teleporting team members calling them out by $target name to teleport them letting them aware they are about to be teleported etc. So many uses. I can't think of a game even today that has such a thing.
Currently I am dabbling with the idea of using macros in Paragon Chat to make a more stream line in game role playing but more structured like a table top RPG but of course utilizing in game dice rolls and animations and the like for visual spiffyness.