When I first started playing during The Burning Crusade, I had no idea what a macro was. I'd love to pretend that this was because World of Warcraft was simpler back then and that a good player could get away with never using a macro. Unfortunately, that isn't the case; I just wasn't a very good player in my shaman's youth.
The truth is that macros are something that any serious raider or PvPer should never be without. They fulfill a variety of roles, from cast sequence shock macros saving you some bar space to using your Feral Spirits' Bash ability on a focused healer to interrupt their Tranquility cast. In a raiding game where the ability to interrupt a target you're not DPSing is a huge asset, learning to manage your abilities through macros is a huge benefit for you and for your raid group (as well as for your arena team).