-the ability to play anything from big damn heroes to scrungey hobos taking jobs to get by in a world that doesn't give a damn and never will (at least at lowish levels)
(Well, the former at high level and the latter at low, at least)
But, 5e, having finally divorced magic items, and thus character wealth, entirely from advancement, really enables the latter to an unprecedented degree, and at all levels.
Think about it, in 4e & 3e you have wealth/level. In 4e, you can turn on inherent bonuses, say screw magic items, be as stingy as you like with treasure - but, the sheer overwhelming ultra-competence of high-level skill bonuses will make the idea of the world treating them as nobodies pretty strained. In 3e, you also nominally have that option, though it's less practical, and, again, high skill checks let the PC shine, and, in fact, /literally make money/ (XOMG! You can, like, make an honest living!) Prior to 3e, magic items were necessary for general functionality in play, and treasure was inconsistently tied to xp/levels in a variety of ways, PCs might be rich, or they might have gold slip through their fingers by the ton, but they'd never be hardscrabble mercenaries their whole career, and, indeed, were expected to be come lords, and land-holders and guild-masters and the like.
In 5e, a high-level PC does not have useful civilian skills - or any skills - amazingly far in advance of an ordinary, particularly skilled professional. But they do have tons of hps. So, if poverty-stricken, the mercenary life is a natural. OK, casters may, depending on the details of the setting, be able to parlay spells into gold in any number of ways. But, also posit a world where honest folk are suspicious/hostile of magic, and, again, it's start blowing things up for those who need merks, or starve. It's really kinda an accomplishment.
Though, TBH, I've yet to try running anything of the sort, nor seen or heard of anyone else doing so, it's a style/sub-genre that is now more doable than ever before.
