Getting everyone on the same page helps avoid confusion. It’s valuable from a knowledge and a social perspective. It allows people to participate. In any case there’s a spectrum of understanding that is created by context. We can use localized (to the conversation) meanings to communicate effectively.
It can, however, become a problem if using the word in a localized way makes communication less clear.
@Thudlow_Boink mentioned a few examples that could be illustrative.
If someone says “I don’t like bugs”… it’s fair to assume that they are not talking about a subset of insects, but of all arthropods, or at least the non-aquatic ones. Context makes the meaning clear, and there’s no need to get nitpicky. There’s also no need to assume the speaker doesn’t know that there are more precise categorizations of creepy-crawlies. That kind of accuracy is just not relevant to the conversation.
What about “I don’t like juice”? A little trickier. Is Hawaiian Punch juice? Maybe? Is juice a beverage that tastes like fruit? That contains > 0% fruit in it? Can carbonated beverages be juices? Is it about the percentage of sugar?
These questions might or might not matter depending on the context in which we hear “I don’t like juice”. If I’m hosting a party and a guest tells me that in advance, no problem. We’ve got a number of beverages that clearly are nowhere the definition of ‘juice’, so I don’t actually need to know the specifics.
However, if a guest says “I’m vegetarian”, I might need to know whether their definition of vegetarian is ok with dairy or eggs. It doesn’t matter so much that they use some precise definition of vegetarian, as long as they can communicate what it means to them.
I’m a good enough host that I know to interrogate people’s dietary labels because it is often important or necessary for them, and I want to get it right. But there are those who don’t understand that there are words that change meaning depending on who is using them.
I know plenty of people who will serve chicken stock to vegetarians, not because they are sinister, but because they cannot understand that vegetarianism is not simply “I will not eat pieces of flesh.”
So much of our language is about abstraction, and whenever there’s abstraction, there is room for misunderstanding.
This was kind of rambling, but the tl;dr is that pedants who refuse to understand other people unless those others conform to a particular language choice are annoying. And, those who refuse to get specific or clarify their own meaning in the face of questioning can be equally annoying. Both types are aggressively fighting against clear communication in their own ways.