I think much of it depends on the personality types, and as stated earlier, the goals of each member.
My current band is pretty much a democracy. Our singer is responsible for the lion's share of the bookings, but each member has the authority to book. This is especially practical since all of our members are spread out across different counties, so each of us is familiar with the clubs in our respective areas. Any major decisions (hiring/firing, money allocation, accepting non-paying gigs, ect.) is done democratically. All band expenses (website, t-shirts, banner, stickers, ect.) are paid right off the top from money earned gigging, so nobody has a financial obligation outside of money earned from shows. We either use in-house production or hire a production company, so there's no PA politics.
The reason this machine works so well is because everyone is on the same page. All of us are accomplished musicians and we all act like professionals. Everyone learns their parts for practice, and everyone gives 100% at a show. If an issue comes up, we discuss it like adults instead of getting pissed off. We actually fired a drummer a few months ago. Part of the reason for this decision was not only because of his playing (he had a tendency to rush, overplay, play out of time, miss fills, ect.) but also because of his attitude. He was taking it upon himself to make bad business decisions concerning the band.
I've been in situations where a designated leader was needed. Musicians might have been lazy or unprofessinal. Now if I were in a situation like that, I would probaly just quit. I'm not old, but I don't have time to work with unprofessional players.