As something of an alt-o-holic, I can't help but have at least one secondary character, just for fun. It's very disappointing that FFXIV discourages this, both by eschewing any sort of cross-character item/gil storage, and by financially rewarding people for only having one character. Still, there are reasons why rolling an alt is still justified:
- Some people just like to look at a different character, with a different "feel," from time to time. I'm not an RP-er, but I do tend to attach some kind of vague personality or traits to my characters. I just get in a different mindset about what that character is "good at," even if it's only imaginary. For example, I have one character who will focus primarily on mage-style caster classes/jobs -- and another who will focus on pugilist, archer, and other more physically-minded stuff. And personally, I gotta have an elezen and a miqo'te. That's just how it is.
- If I have a full-fledged summoner, decked out in cloth caster gear, and a bunch of other magical cross-class spells, it's not necessarily going to make leveling a heavily-armored melée class any faster. I'll get the cross-class skills (those that apply, anyway) but I still need to level, get gear, do my class quests, etc. It's a lot like rolling a new character anyway.
- While you're playing one character, the other is always gaining rested XP.
- You can choose a different starting city, and a different grand company when the time comes.
- If you have something useful that you really want to give to your alt, you could potentially "launder" it through your FC's storage. I wouldn't do this with a high volume of goods, as it's likely to raise some red flags with your FC (and you always risk someone else nabbing it). Still, if you can craft something nice that isn't necessarily nice for the character who's making it right now, you can send it off to your alt. You have to make gear to level your crafting anyway -- might as well put it to use.
- Let's be honest, most people aren't going to level every class to 50 and have best-in-slot gear for everything. And there's really not much reason to, anyway. When you're in a dungeon as a Black Mage, it's not like if the tank drops out you can just switch over to your Paladin and take over. Aside from a small trifle of Square Enix-approved cross-class skills, having other classes leveled on one character means basically nothing in a mid-to-high level instance. You might as well not even have done it.
- Not having to keep gear for all classes on one character will help manage Armory/Inventory clutter.
- Story quests that give you gear as a reward only let you pick one piece. If you took the caster robes, it's not like your gladiator will know what to do with them later. If you're questing on a new character, though, you are free to choose whatever suits their desired specialty.
- If you have friends/contacts who aren't all on the same server, you can have an alt or two just so you can play with whomever happens to be online at the time.