Commonly used. I guess that it is most commonly used when people want a superlative, when they want to say something is the extreme of something and there is not superlative form of the adjective. He is fast, but Peter is faster & Dave is fastest. They are all ambitious, but Helen is the most ambitious of all of them. ( There is no word ambitious-est) I wash my car any day of the week, but most often on Saturdays. . These ones seems a little different. How much cake do you want? Give me most of it. = A piece greater than half. Was the test easy? Yes, Most of it was ok. . Or were you asking about "How many times" ?