From my experience threads could be locked for many reasons such as Mod Review, Hopelessly Off Topic, Question Asked and Answered, Bickering, Illegal Topic, etc...
Posts may be removed for language, calling out, inappropriate, poor taste, graphic, offensive, inappropriate links, etc.
Posters banned for blatant and repeated rule violation, spam, advertising, linking to competing sites, lack of decorum, etc...
any
Many are black and white and just as many are judgement calls...
Also worthy of mention is all of the above by mistake... how many have reported a thread not meaning to or as a mod pressed the wrong key by accident?