There’s this magical thing that happens when you’re a verbal processor like I am. I get stuck on a chapter, have a vague sense of where I want to go with it, but am really struggling with how to get from A to B in a way that’s believable yet interesting. So I enlist one of my betas (I have the finest betas in the land, for the record) to help me brainstorm through it, and some magic of cooperative energy happens. And I think half of it is their stellar insight and ideas, and the other half is their good questions and listening ear that help me sort it out by virtue of having someone with whom I can process. And all this is on top of the proof-reading, the objective eye, the differing perspectives that help me get out of my head so I can find out how the story works to anyone but myself before it goes public.
If you don’t use a beta, I highly recommend it! I didn’t used to, and I’m so much better off now for having them. And even if you don’t feel the need to have your work pre-screened, you should at least have someone with whom you can brainstorm your story throughout its conception. No one is an island! :)