In a certain informal speech style (the same one that uses 'like' frequently?), speakers often use tags like "you know" and "i mean," perhaps to check that the listener is following.
Consider Scott's recent observation: after any sentence, it is possible to meaningfully insert the phrase "you know what i'm trying to say." For example, "i think you're great. you know what i'm trying to say" or "the sky is blue... you know what i'm trying to say" or even "the taste of mango... you know what i'm trying to say?"
and this is the vagueness and power of language. we don't say things in the interest of logic or truth; we speak so that people will know what we're trying to say. each word or phrase is a stand-in for all the things we know we can never describe.
articulation is a personal favorite example. it is impossible to describe the condition of the tongue in real time, because as we speak, it moves, and we can never catch up with it. so we generalize to statements like: "every time i laugh, the base of my tongue hurts." here we've used language to simplify our experience into cause and effect (or at least correlated events) that recurr in patterns. if my statement isn't true EVERY time i laugh, or the pain is a little different each time, it's ok because you know basically what i'm trying to say.