In my case, i login to add accessories, chk for firmware update, and set automation. Other than tht, i don’t use it.

As for automation, it works differently. Obviously Aqara app has some features tht are not exposed to Homekit. The Aqara motion sensor, for example, has an ambient/light sensor tht is not exposed to Homekit. So, if u want to switch on a lightbulb when a motion is detected and it is dark, Aqara app can do that. Home app won’t be able to detect ambient lighting condition (using Aqara motion sensor) so automation in Home app will turn on the lightbulb when motion is detected.

Hope my input above helps.