I have two level 80 characters. I don't talk much about my alt, Khelark, but she's pretty great for an alt. While she is fun to play in her own right, she is mainly there to support Kheldul.
1) She makes all the serious money. She does it by "creating value". She's got tons of gem cuts. She usually has between a half-dozen and dozen uncut epic gems of every flavor in her inventory. She supplies AH with a steady stream of the things people need at a reasonable profit.
2) She is often camped at the Auction House. She makes sure Kheldul has ammo, flasks, speed pots, and even health pots.
3) She makes sure Kheldul has all the right epic gems he needs in the mail for dps and pet-tanking... often fetch-able during a raid thanks to Knight Kheldul's other loyal supporting squire. And if Kheldul gets some loot on a Wednesday, Khelark just buys him the suitable enchant if nobody is available to do it, before the Thursday raid.
4) While she has bought herself a few nice things (1, 2, 3) for 9-12k gold each, she gives Kheldul plenty of goodies -- some that even have very useful effects.
5) She converted plenty of things to BoA honor tokens and sent them to Kheldul so he could get honor gear twice as fast.
6) Finally, she supports Kheldul as a release valve. If I want to do a PUG, a 5.4k gearscore healer can get an invite pretty quick. I don't have to worry about raid locking my main. I don't have to go over-board focusing on the most minuscule issues on my hunter. A healer can make or break a group. And there are new sometimes unexpected challenges. "Can I heal and dps more than the dps?" Last week, I solo-healed VoA-10 and went on a reasonably successful ICC-25 PUG. I even have proof of doing the easy gunship battle in heroic. Release valves are a good way to keep your main fresh.