knowledge as a social cue

An educated native speaker of English has a vocabulary of about 25,000 words even though only about 6,000 of them account for 95% of what they say. So what is the value of knowing the other 19,000 words? A large vocabulary is a reliable signal that someone has read a lot, because that is the usual way someone comes to know many words. People who read a lot are usually smart; thus, the use of rare words is a signal to other intelligent people that they are alike and should interact. The fact that we have dictionaries (and can instantly look up the definition of words online) does not negate the advantage of having a large vocabulary. 

It's similar to the way people wear certain clothes in order to fit into a group. There's a reason why businessmen always wear suits. It's an advertisement about who they are and wish to associate with. 

Indeed, the most common way people try to ingratiate themselves into a group is by changing their appearance and sometimes their speech. People who move to a different country or region often adopt the accent there in order to be accepted. 

Knowledge also works as a social cue. Most knowledge, especially the kind from formal education, has little direct utility, especially today when almost everyone has the internet in their pocket. The amount of practical knowledge a typical adult needs is surprisingly small. Almost all the rest functions as way to show interests and status. For example, knowing how to change a tire is a lot more useful than being able to read Latin, yet knowing Latin is a clear indicator that someone is inquisitive, well-read, and probably intelligent. I suspect this is the reason the high IQ society Mensa uses a Latin word for its name.

Someone who is very knowledgeable and demonstrates it is showing (unintentionally or not) who they are and who they want to associate with. This is why people should be careful about what knowledge they share. If you talk about astronomy all the time, people will wonder why you aren't working at a planetarium or a member of a stargazer club. Sharing knowledge on different topics sends mixed signals, sort of like switching from one language to another. If you want to speak English, it does no good to go around speaking Spanish or any other language. 

Still, being knowledgeable on many topics is generally respected. Scholars hundreds of years ago were respected precisely because it was known to take a lifetime of study to learn so much. The key to avoid being called a know-it-all is to say little. Sile et philosophus esto is Latin for "be silent and you will pass for a philosopher". In any case, know-it-all refers to someone who pretends to be more knowledgeable than they are. Someone who really does know a lot on many topics is a polymath. 

I say be a renaissance man if you can. The world can always benefit from another genius.

I should add that jokes are the most useful thing to memorize if you want to make friends and get people to like you.