It affects a certain disposition for the writer; the information it contains isn't in the actual data they are expressing, but rather the state of mind that they express it from, which can be important context. Oftentimes it can indicate exasperation, which is an important social queue to be able to pick up on.

A little excerpt from Arlo Guthrie

"I mean, I mean, I mean that just, I'm sittin' here on the bench, I mean I'm sittin here on the Group W bench, because you want to know if I'm moral enough to join the army, burn women, kids, houses and villages after being a litterbug."

Imagine that without the "I mean"s in it, and the importance of how they convey his stance on the situation.