I think these days the emphasis has changed a bit from "required reviews" (more senior dev or peer signs off on code) to "request review" (developer __wants__ the review, because it's a good learning experience and a way to share responsibility for the code (and any problems it might cause down the line).

Anecdotal, but I feel like I see more teams where that "Merge" button is available to most people, but in general doesn't get pressed until the code has at least one review, whereas before it was often only accessible to a select few, or a review was required before it activated.