I have the great luxury of a hairdresser who comes to my house. Midway through the process, Cindy and I have tea and chat or I read to her from the book I'm working on. Today I read a section of dialog that I wrote about a month ago. And as I was reading it to her, I realized three things. That the dialog was pretty good (feasible, natural, well paced). Second, it goes on too long and that's because of number 3. I don't have a good enough reason for it.
I wanted this dialog to show a conflict between the roommates in the flat and I wanted to make the protagonist defend her shady boyfriend. And I realized in reading it aloud that while those two things happened, I took too long to do it. So I either need to find another plot or character point to include in that dialog or cut it short.
I don't think I would have discovered this in a silent reading of the text. However, I now realize I might have skipped over some of it in a silent read. And if the author doesn't find it interesting, yikes! How will the reader? So I pegged that for reworking.
So two bits of advice: Read your work aloud to a trusted friend and listen for your own impatience. Second, watch for places you're tempted to bypass in a silent reading. Maybe they can be shortened or eliminated all together.