I agree that most of the time "you know" is meaningless filler, and as such is quite overused, but there are also other uses.
"You know" can be used to refer to an idea that may be difficult or tedious to express in words but that the speaker thinks is relatable, so in this context it means "if you catch the gist of what I'm saying, I'll omit the explanation" or "do you relate with what I'm describing?". This can indicate that the speaker is unable to express the idea in words or simply does not wish to. For example,
So I'm walking home from work, when all of a sudden I get this tingly feeling, you know? Like someone's watching me.
Person A: Why didn't you tell your wife about it?
Person B: Oh, you know... it's complicated.
It can also mean "I think you should know" or "for your information". Examples:
You know, if you don't shape up soon, I might be forced to fire you.
If you keep doing that, you'll catch a cold, you know.
It can also mean "come to think of it" when introducing a sentence:
You know, that's really not a bad idea.