To play devil's advocate:

HRM make sense to me for recreational riders if they use it to slow their rides down. It's a strong tendency even for duffers to speed up during a nice ride and push too hard when you shouldn't.

But wattage calculations seem pointless to me.

My nemesis is hills, of which there are a bountiful supply in my area. When I'm going up one, feeling the searing pain in my legs, seeing blood trickle out of my ears, and developing tunnel vision with a figure dressed in Gleaming White calling out my name and entreating me to come Home, I can't imagine knowing that that happened at 250W instead of 245W like the last ride being useful information.