It'd be a bit weird to say Roman Reigns benefited from the kicking Brock Lesnar doled out at WrestleMania 34, but think of it this way: Roman was spared the indignity of having another 'Mania celebration booed out of the building (like at WrestleMania 32 and 33), and fans were saved from a "happy ending" few wanted.
In the long run, Reigns will be helped by not beating Brock, and it's not as though he wasn't protected; the guy kicked out of multiple F-5's, left Lesnar seeking advice from a bewildered Paul Heyman, and was written to look borderline superhuman - all ahead of transitioning smoothly into a Steel Cage rematch with Brock and enticing feud with Samoa Joe.
Naturally, given the spotlight of success, it's mainly winners who came out of WrestleMania 34 looking the best. That's not true across the board however, because even some who lost did so for a reason, and they ended up in a more advantageous position going forward. And there was one superstar who benefited just for being back amongst the action. It pays to say, "Yes!"