I've been doing bare-metal embedded for a long time now, and believe me, I don't want to be the negative guy, but I stopped the video at the third "the compiler

I've been doing bare-metal embedded for a long time now, and believe me, I don't want to be the negative guy, but I stopped the video at the third "the compiler inserts runtime checks". A thing I don't want in my embedded code is more hidden code. Runtime check is, in my opinion, a pretty bad selling point for embedded (bare-metal). What is this runtime check the compiler inserts? How much does it costs? If the anwer goes into the "you can disable it" or "some things are infered and some other are not" territory, then I guess I can keep the good ol' C as the main referrer for embedded.