My team basically has their dps on buttons 1-4.
1 is Lightning Bolt.
2 is Lava Burst.
3 is Flame Shock.
4 is Chain Lighting.

The paladin has a Holy Shield, Hammer of the Righteous, Judgement macro on keys 1-4.

When my fourth shammy is resto, her 1-4 keys only fire off with mod:alt.
Basically if I press 1-4 with ALT she will also cast that spell.
Clicking it without ALT and the resto will not cast any dps.
So if I need to heal, I can freely mash buttons 1-4, while free to heal without DPS casting as she wants to get a heal off.
If heals are ok, but I want her resto instead of a 4th Elemental, Alt 1-4 and she joins in the nukage.

There are a lot of options to consider.
Find something that works for you.