For example, some LeetCode questions are textbook problems. You really should familiarize yourself with them, but you will probably never see them verbatim on an interview. Other LeetCode questions are too tedious or time-consuming to do on a whiteboard in an hour. You will also not see them on an interview. For some people they can be fun brain-teasers, but if what you want from LeetCode is time-efficient prep material, you need to be able to tell apart these three kinds of questions.
If you look at comments on LeetCode questions, you will immediately discover that tons of people treat LeetCode as a pissing contest for its own sake. Should it matter that your solution runs in 18 milliseconds and theirs runs in 15? Or that they code-golfed theirs into 200 characters? Probably not. On the other hand, most canonical problems do have canonical solutions, and you should probably know what they are.
Knowing what to take from LeetCode and what to leave is almost its own discipline.