It's hard to say exactly what they moderate or how.
If you write in a less spoken language Facebook struggle to moderate you. Unless you’re trying to sell animals, because they spot that in seconds.
Facebook is happy to let bad content stay and profit off it unless said content carries a risk of bringing bad PR; I'm assuming this is the case with the "selling animals" thing because some animal rights groups escalated the issue to the media, and it is now the case with anything Trump- or election-related (not that I'm defending said content, but pointing out that its removal is for PR reasons as opposed to Facebook actually caring about democracy or discouraging violence).
However, it's clear they aren't acting in good faith and aren't actually interested in moderating bad content. Cybercrime-related Facebook groups which don't even attempt to conceal themselves are commonplace on Facebook: https://krebsonsecurity.com/2019/04/a-year-later-cybercrime-... despite detecting them being trivial based on a simple keyword match.
Facebook moderates content only when it draws too much attention, but either way Facebook profits off said content as their algorithms promote it (because said content generates "engagement").