This. When rehearsing in your head, it's easy to gloss over parts that really need some working. When treating it as a proper presentation, those spots are painfully obvious. Better to find them alone, even if watching yourself is a bit awkward.

I also like to record myself because sometimes I find a good way to explain something, which I want to remember and explain the same way during my talk. It also helps with pacing. Am I too slow or too fast?