You’re right in that running HA just for a WoL timer would be silly, but (presumably) it’s already running for other, less silly purposes.
I’d say the main benefit is when the machine requires regular (as in daily) reboots, or if it’s something you don’t trust is fully private and want to be powered off outside work hours. Not useful for me, but I can see why it would be handy.
Is dumb doorbell + separate CCTV camera a valid alternative? Even my fairly basic Reolink camera has a much better image quality than any doorbell camera I’ve seen, and HA can pull an image from it and push it to my phone in only a few tenths of a second whenever someone pushes the doorbell.