Usually when bands split up, you find out Who Really Had The Talent In The Group. It's not always a surprise, either: does anyone really remember Andy Summers' or Stewart Copeland's post-Police work? Thought not. And while Genesis did put out some decent songs after Peter Gabriel departed, and almost certainly sold more records than he did, it's pretty clear who's the stronger artist. Bauhaus' split made it obvious that Everyone Who Wasn't Peter Murphy Had The Talent In The Band: I'm not a huge Love & Rockets fan, but comparing them to Murphy's solo work, I think it's pretty clear who won in that particular squabble. Other examples, off the top of my head: Billy Idol vs. anyone else who was in Gen X; Don Henley vs. anyone else who was in The Eagles; Simon vs. Garfunkel; George Michael vs.... um... y'know... wossname*.
(Mind you, I'm not arguing that Billy Idol, just fr'instance, is necessarily a huge artistic talent. But you almost certainly know who he is, and you might just possibly now be humming one of his songs only because I mentioned his name, and you'd need to be fairly hard-core to know the name of any of the other members of Gen X. Same thing for Henley and the Eagles — okay, Glenn Frey had *one* relatively dire solo hit, but Henley put a lot of songs in the charts, and some of them were pretty good.)
Somewhat less often, but still pretty commonly, you find out that in fact Nobody Really H.T.T.I.T.G. — that there was something synergistic about that specific line-up which allowed them to achieve heights well beyond the capabilities of the individuals involved. Without too much overstatement, I think it's fair to say that none of the four ex-Beatles ever even got close to the level of their work as a group. Once Roger Waters left Pink Floyd, neither he nor they managed to make an even half-decent album in more than a quarter-century of trying. Ultravox goes in this bucket, as do Tears For Fears, Led Zeppelin, The Cars, Pixies — all great together, all pretty insignificant once the band-members separated. Duran Duran weren't even that great together, but the drop in quality once they fractured is still noticeable (though I admit to a guilty enjoyment of the two Power Station singles). For that matter, I'm not even all that crazy about the work of Marr or Mozza outside of the Smiths.
But then very rarely you get those unusual bands in which it turns out that Practically Everybody Really H.T.T.I.T.G. I'm thinking of Wire here (Colin Newman, Graham Lewis and Bruce Gilbert have all done sterling solo work), and the Depeche Mode -> Yazoo -> Erasure/Alison Moyet family tree is a pretty good illustration, too, but there's an even more striking example which I often forget: The Beat (or "The English Beat" in the USA) were an obscure but great ska-pop band who fissioned into two higher-profile great pop bands, General Public and Fine Young Cannibals. I'm not sure I can name any other group that did so well (artistically or financially) by splitting.
*...Andrew Ridgeley, damnit.