the only reason i prefer medium rare STRICTLY is because of the fat
scientifically speaking (and if someone wants to correct me here, go ahead; this is information i learned a while ago and i may have forgotten some of it) medium rare - that being 130-135F/55-57C (granted as low as 53C can be medium rare too) - is the point wherein the internal fat of the meat only just begins to render into its juice form but doesn't start to evaporate from the heat. any higher than medium rare temps and the fat begins to evaporate, while any lower (im talking 51c or below really) and the fat doesn't quite start the process of rendering.
this is why well done steak is chewy and dry because by the time you cook it to that temperature, all of the internal fat has exited its solid state, entered its liquid state, and seeped out of the meat into the pan only to be sent to oblivion itself. the only time where this isnt the case is if that's a
VERY fatty piece of meat and there's too much internal fat to actually be seared off by the time it reaches 71C (well done temp)
note im saying
INTERNAL fat. internal fat is the little marbling you see throughout;
that's the stuff that renders.
while yes, the external fat cap like above what's circled will also render, it's typically far denser fat and u should really only keep that on if the steak isn't well marbled because then the fat cap can provide some much needed juice. there
IS such a thing as a steak that's too fatty though. fat caps on more expensive cuts can also be a little too strong in flavour, like wagyu fat caps which are liable to make you vomit out of sheer flavour intensity unless you have a strong stomach for that.