I mostly agree with everyone on this thread, I use bullpen by committee on every single team except one and I'll explain why. Never say NEVER because certain times a closer can be value-added you just have to understand the reference points you are adding to.
Player Profile: Mike Prinz is a Hall of Fame caliber setup, and it's important to understand why and what settings to use. His dur + Stam means if I set his target pitch to none and Max pitch to 25, he can throw 1.2 innings 2 out of 3 days and sometimes 3 out of 4. This is manifested in his career stats, he has a huge volume of appearances with about 1.2 IP/game. He also has an excellent W-L record with substantial saves, he could get 125 wins and 250 saves which I think may be unprecedented in real life for a true reliever (non-Smoltz). Guys are supposed to get one or the other but not both
BUT I don't just want innings for the sake of innings. IMO it's a bit cavalier to say "use him as SUA to get him a ton of high leverage innings" because that's honestly not true, there's a ton of fluff in there esp when you're winning by like 4-5 simmy isn't smart enough to leave him on the bench and save him for the next day or a smaller lead if your SuB starts blowing it.
Also Prinz is great at starting innings but not great at jams that he or others created because he's bad at strikeouts, so inherited runners score on him at a higher rate. So I do have his call bullpen at 2 or sometimes 3 to have somebody else relieve him in certain spots.
On the other hand,
Player Profile: Louie Kondou is a true closer. His dur + Stam make his Max pitch count either 15 or 20. The average pitches it takes for 1.0 IP is about 18, for elite guys it's about 15.5 or 16. Since you obviously can't control it, I tend to do Max 20 which tires him out faster, I can get about 2 out of every 3 games but sometimes less.
He can not and should not be pitching more innings per appearance, this player is purely a 1.0 IP pitcher nothing more nothing less. There is no higher leverage situation than late & winning or late & tied
It is also important to understand how often closers should be saving games in general. A 3-run 1.0 IP save is successful about 94% of the time by default, a 1-run 1.0 save about 80ish%. So the value added is a higher save percentage. 384/422 is 91% which is very very high for HBD, he is basically treating every lead like a 3-run lead.
Also understand the his W-L ratio is value added. If you notice in HOF voting, closers are almost always in a negative ratio because they're not designed to win, they're only designed to blow a save and lose. But Kondou is 46-41, 41 losses in 716 appearances (5.7%!!!) where you know for a fact the game is close is ridiculously low, it's astonishing. That number doesn't even make sense.
So yes, closer can be cool but it has to be under very specific circumstances