Well, english speaking school kids use them all the time to look up spellings and definitions. My 12 year old native english speaking son just spent two hours doing his english homework looking up words in an online dictionary and writing definitions. Is that different in Poland?
Well, with Polish orthography I guess that some pupils may need to check the dictionary often, so maybe there were also homeworks like that... I may not remember because that was always my strong side. I don't remember checking any definitions.
I think that at the age of 12 we learn about stuff like adverbials, grammatical objects, and grammatical modifiers and that's about the end of learning the language in school. Everything later is literature.
No one is that good they do not need to check, and one of my biggest problems editing translations is that translators commonly think they already know, and do not need to check. As an engineer, we always had reference sources around to confirm our beliefs, because in engineering one cannot bla bla bla away a mistake, because Mother Nature is always the final decider. And that is the most basic problem in the linguistics trades.