But what can it do more easily than an mid 20th century home can do?

One word: Automations. Everything from lights to irrigation, HVAC to surveillance cameras, fishtanks to plant monitoring, managed by a single, extensible open source platform, hosted locally in your own home.

Of course that is not trivial. If you don’t see your smart home as a hobby you enjoy putting time and effort into then the smart home scene is not for you, especially not Home Assistant.

Sounds like you are in a fine place with your home, so you are probably not the target audience here.