As you start off you really don't need any macros outside of the follow, assist and what not but as you gain more spells you want them. An example could be a frost mage, early levels frostbolt does fine but eventually you might want to add in casting icy veins and summoning a water elemental and telling it to attack. Later on you may find use for modifiers in macros to condense the amount of keys you need bound which is what macros offer as well. If you running a mage and/or druid I'd suggest setting up a focus key for them so they can use their cc's to do this you'll need some macros.

As for the healing while continuing to dps question. I split my keys up so that I have 1-2 keys bound for dps buttons while having some others dedicated to healing or tanking. Here's my setup, I use the numpad for almost all of my functions:

num0 = /assist party1 (this is on all characters)
num1 = my paladins avenger's shield + consecration and nothing on my other characters
num2 = my teams dps macros and outof combat temp buffs like seals
num3 = nothing atm
num4 = nothing on all characters except for the priest who shields the tank then penance
num5 = nothing on all characters except for the priest who spams flash heal
num6 = priests holy nova + trinket use
num7 = teams buff button
num8 = shaman totem
num9 = priest fade pally taunt
num- = /follow on al toons
num. = set mage focus
num_enter = sheep mage focus

As you can see going into combat I use num1 then spam num2. If tank needs heals I use num4 and num5. If the party needs heals I use num6. This way I can heal, dps and tank with minimal keys needing to be pressed. I am finding that soon I will need individual heal keys as dmg can happen elsewhere than to my tank. My teams at 65 atm and has leveled running nothing but instances.