What immediate placement is actually buying
Two things, and they are worth separating. The first is time and surgery: one procedure instead of two, and months removed from the sequence. The second is tissue. A socket left empty changes shape as it heals, and the soft tissue follows the bone underneath it. Placing an implant and a provisional crown immediately gives that tissue something to hold its shape against while it heals, which is why the aesthetic findings in the evidence favour it.
What it does not buy is a shortcut past the biology. The implant still has to integrate with bone, and that takes the same months it always did. The provisional crown fitted on the day is out of the bite while that happens. Same-day teeth and same-day function are different claims, and only the first one is being made.