off meta is not about skill. it's about who you're facing. off meta is safer taken in the last 2 picks of the champion selection draft. when you play off meta you're taking advantage of the particular trait your champion possesses and using it in a literal or metaphorical way that was either not intended or was intended, but has become unpopular due to missing pieces or overwhelming deficits.
skill is not anymore a factor than when playing meta. if you play something you're unfamiliar with then you're likely to lose regardless of whether you're playing braum jungle or zac jungle. it takes time to read those descriptions and a lot of times (especially right after updates) they're incorrect.
for newer players without a lot of knowledge about the game there are generalized champions that do exactly what you'd expect and do it decently, but not so well that you'd be able to afk and let your cat play while you watch reruns of naruto.
the rest of the champions have some slight variances. some have item dependencies and others have build dependencies and even more have role dependencies or lane opponent/ally dependencies. to that end you're better off picking one of these champions only if you know their kits fully.
off-meta simply means that whoever is assumed to have the best current patch synergy will be meta and you pick someone who is not that pick or a generalized champion. for whatever reason.
patches are not static and are released roughly every 2 weeks or so. which means that the meta changes every 2 weeks. however the players on the pbe get to experiment with pre-release stuff and as such the patch is usually expected to create some sort of specific environment. so a meta will be created without actually knowing if it will translate 100%. due to that minor inconsistency and the small lifespan of a patch it's possible for things to happen that can surprise the player base.
for the most part though the reason for off-meta choices should be and is for a strategic advantage.
(just a goofy example) didn't work was not because your jungler spent more time bot and mid than trying to salvage your 0/9/2 top lane by the 6 minute mark...
