I am a 1st year PhD student. I got a bachelor's degree in CS but I didn't start learning TCS systematically until this year.
This dumb question came to me when I opened an undergrad complexity lecture watchlist after I forgot it for months, and realized that I had already learned the content from an "advanced" textbook. And I found things covered by the course were learned by myself within a much shorter time. That's perhaps a special case. But I noticed that undergraduate-level courses/materials cover more details and examples about the basic concepts than advanced ones, and I don't know if it's necessary to know such a kind of details.
So my real question starts here: should one skip undergraduate-level TCS courses/materials to save time, or do it step by step to reinforce knowledge?