I would speculate that for each raid team you add to a guild you multiply the complexity of difficulties and coordination exponentially. My guild runs two raids as many guilds do. We have a primary team and a casual / alts weekend raid.
I had a long-standing player in the guild wanting to create another leader-team because the leader-team is full and he failed to sign-up and the causal team wasn't advanced enough for his wants.
While, in practice, this sounds like a quite reasonable request. Here are the problems another leading team can cause, if you cannot coordinate properly.
- If the teams are on different schedules, you have doubled the competition within the guild for people wanting the schedule that is more to their liking.
- If the teams are on the same schedules, you have decide how important it is to the guild that both teams advance equally. If it's important you'll have to balance participants and people want to raid with friends. It can't be about just numbers.
- You have the potential that teams can compete for the "better players".
I'm not saying it can't be done. I know there are more hard-core guilds that make this happen.
I'm just saying that it has drawbacks, issues and more "work" to make it happen.
If your guild does this... what approach do you use?