For me, it's a little like feeding coral, or having a rich environment for enzymes to operate on: if my thinking is ready for particular new insight, it's great if that idea comes along. It then becomes a part of my thinking. Similarly, if I'm working on a problem, I often get insight from other activities, including reading.

Reading well-written books and essays influences the way I express myself, unconsciously.

I also think it keeps the mind supple, to be able to absorb new perspectives. Perhaps even more important, is to be reminded that they are things I don't know, and didn't even suspect (the particular things aren't so important, just feeling of not knowing as much as I thought.)