Tbh I always walk out of a lecture better and better understand stuff if I have read the content beforehand.
That's simply because it gives me the mindset of what I don't understand and what to pay attention to in particular. Also the lecture might reinforce stuff that you don't get. It is better to get lost and spend 20 minutes before a lecture figuring something out than actually spending 20 minutes in the lecture confused what is even going on and also losing track of the other content introduced afterwards.