Verbalizing your thought process is invaluable for validating that what you are doing/thinking actually makes sense. For developers, just think about all the times you have started explaining some code problem to a colleague, and instantly come upon the solution, simply by verbalizing ideas. The other person doesn't even have to say anything. There is even the concept of 'rubberduck debugging', where you explain things to a rubber duck, and it helps solve the problem.

I have often thought about what the experience would be of living entirely without verbalized thoughts. Like, obviously ideas and concepts exist separately from their verbal representations, so skipping words would be a more pure and effective form of thinking, right? But lately I have come to the belief that words are a necessary scaffold for organizing more complex ideas. Without them, I think we would simply be unable to put together complex enough models to understand things at the level we need to function in our complicated world. Like making diagrams helps with analysing domains.

It is proven that lack of verbal stimulation leads to slower develoment in children, possibly for the same reason. I think it is also the mechanism by which people who spend a lot of time alone (think castaways) eventually go insane - due to the lack of an external validation mechanism.

This understanding would seem to indicate that people who don't have an internal monologue would be less capable of expressing/understanding complex ideas. I would be very interested in knowing if that is the case.