Two anecdotes are relevant here.

Lewis Carroll from the introduction to his Symbolic Logic:

If possible, find some genial friend, who will read the book along with you, and will talk over the difficulties with you. Talking is a wonderful smoother-over of difficulties. When I come upon anything——in Logic or in any other hard subject——that entirely puzzles me, I find it a capital plan to talk it over, aloud, even when I am all alone. One can explain things so clearly to one’s self! And then, you know, one is so patient with one’s self: one never gets irritated at one’s own stupidity!

And Henry Hazlitt from his Thinking As a Science:

Fortunately there is one method superior to any yet named, which requires no study before its application, and no paraphernalia during it. It consists in simply talking your thoughts as you think them. One who has not tried this can have no idea of its effect. It possesses almost all the advantages of writing. You cannot wander without realizing the fact immediately. It makes your thinking much less vague than if you thought silently, increases your vocabulary, always keeps pace with your ideas, and requires practically no attention.

It may be objected that silent thinking itself is put in unspoken words. But this is not true. Part of silent thinking consists of unspoken words, but part of it consists of images, concepts and attitudes which pass through our minds and which we do not take the trouble to name. In silent thinking, too, there are also what appear to be occasional dead stops. All these processes drift into each other indefinably and are unrecognizable. When we talk we realize whether our images or concepts are vague or definite by our ability to name them, and we realize when our thought comes to a ^ dead stop' by the fact that we miss the sound of our own voice.

[...] Talking has one disadvantage — it cannot always be used. To practice it, you must either lock yourself up in your room, or sit alone in a forest or field, or walk along unfrequented streets and by-ways. You can by no means allow any one to hear or see you talking to yourself. If you are caught doing this some asinine idiot is sure to mistake you for one.