Why the use of a Indirect object pronoun ?
When referring to quedar as "fitting good": Why is it " Le queda bien", not " Lo queda bien" ? to express " it fits him good". Seems to me that "he" is being directly affected by the whats fitting him, hence a DO. Thanks !
4 Answers
In English "fit" can be either transitive or intransitive. e.g. (trans) Make the punishment fit the crime. (int) These shoes fit (me). When used transitively, the meaning is to alter/modify something so as to make it more suitable. In "These shoes fit me.", the shoes are not changing/altering me (or anything else) but that their size/shape is suitable for me.
Quedar is an intransitive verb, so it doesn't have a direct object. The person is the beneficiary of the act, so he is th indirect object. The thing "fitting him" is the subject.
I'm afraid I'm not very good at explaining this but look at this example:
Las botas me quedan grandes.
I would say that the boots are the direct object because they are the things fitting (ie the verb quedar is referring to them - (ie: they are receiving the action of the verb hence quedan/pl)
and the person 'me' is the indirect object because you're talking about how 'the shoes are fitting' on me?
I'm not sure if that will make any sense to you but thought I'd try 
All the best!
I can't give you a really great answer, but I know in this sense "quedar" ffunctions like "gustar". Actually, according to my professor from Spain, estar can function like this as well when it refers to sizes. Por ejemplo: "Me están grandes los zapatos." This is a really interesting to subject to me, because my friends from other countries don't use this construction.
