What are examples of medically necessary procedures (i.e. not elective plastic surgery or elective botox) that aren't covered? I'd argue that "when I need it"

What are examples of medically necessary procedures (i.e. not elective plastic surgery or elective botox) that aren't covered? I'd argue that "when I need it" is true, for non urgent matters that might not be when I want it. Personally I've had good experiences on the when I want it side too, but I know that does vary a fair bit.