I always thought it was for the other person. It gave them time to prove themselves.
I now think it’s for you. It gives you a moment of hesitation before you presume someone is wrong.
People are rarely 100% wrong. Often they’re just wrong from your point of view. Or perhaps they’re working from older/newer information and one of you will benefit from a conversation. Once you see their perspective and learn their options, “wrong” disappears.
The doubt, then, is to doubt that people are immediately 100% wrong. The benefit is that it gives them space, and helps you maintain respect.
Give yourself the benefit of the doubt.