There are lots of pros of using such approach. Most importantly the anime/manga stays fresh as you're less likely to get bored of the characters. Another huge pro is the ability to kill of one of the protags if you use that approach.
But the examples given on TVTropes are debatable at best. If you want to include all the series which aren't clearly centered around one character... Well, let's just say you'll have a problem with that. I bet there are actually more examples of series where there's more than one protag compared to ones that follow a single person all the time.
‣ If you really can't tell who the protagonists are in LoGH there must be something wrong with you.
‣ Just like they said, Soul Eater has three pairs of protags. The distinction between them and background charaters is very clear, though.
‣ FMA - no, just no. The series is named after it's protagonist. Let's be serious here.
‣ Simoun - not really. The screen time is hardly spread evenly. It's obvious Aaeru is the real protagonist.
‣ DRRR - if we're talking about the anime then again, the time is hardly spread evenly (with Celty/Mikado getting most of it).
I can live with 20th Century Boys, I agree with Baccano! (the joke is the author claims Firo is the protagonist of the series).
If 'ensemble cast' is supposed to mean 'series where all introduced characters are of equal importance' then you'll get somewhere as there aren't thousands of series like that. Of course, most of them will be SoL anime/manga about those 4 schoolgirls.