Is there any reason to have a second party? Other than the difference between an Elf Fighter and a Dwarf Fighter (movement card and race slot) is there any reason to have a back-up party?
For replaying the sp campaign for more items and not having to switch gear to lowbie stuff to be allowed in, being able to complete quests (come after the campaign and have demands on 3x race et c), being able to vary your party in MP - although those don't require you to actually take them through the campaign.
Beyond just race: Because some people like to use double or even triple of one class, at least in a few missions.
Also not just for fun, but for strategy. If you face an enemy that has strong anti-melee defenses, you can render the enemy helpless by bringing in a spare Wizard (to replace a Warrior). If you face an enemy that has strong anti-magic defenses, you can do the reverse. If you face an enemy that cripples your Dwarf character with Encumber effects, you can swap out for an Elf, and so on. If you DON'T have other characters, then you are forced to try to deckbuild against these specific challenges with the narrow options open to your current party. People often view this "changing a party member as part of deckbuilding" strategy as too much effort, and I'll agree it's a lot. But I also am surprised by how many times people say "wow, I was completely failing at Adventure X with my regular party, but then I changed characters and it was a breeze."
making a second team is not as hard and tedious as the first one, because: - you already have some equipment to speed it up - because of how EXP works, if you attempt to fight through campaigns with lvl of 2+ higher than your characters you will get 20 exp! (assuming you got better loot already, it's achievable!)
For me at least, the main reason is for the quests - some of the quests require certain party compositions, all human warriors, all elf mages, etc.
For me, it's both about tackling the different challenges and about trying different playstyles. I have three parties; a balanced one, a 3-mage and a 2-warrior-1priest. All of which offer very different tactical options and added fun.
