extended WiFi to LAN, router --> cAP ac --> LAN clients: works but don't understand 100% why

RouterOS Wireless Networking
6

they are brand new, properly not to justify to buy new ones.
Why should I do it?

it is: WIFI 6 Roadmap - MikroTik


Anyway, that does not answer the questions raised here. Any input in this regard?
Would make me very happy :).