Necessary? Probably not. It will still work without.

If you choose to give the AP a route to the internet then DNS will of course help. System>Packages can't update as it needs to resolve a host name to do work as an example.

What is the use of setting a fixed IP address to an accesspoint? I prefer to have all my IP related stuff done by a DHCP server, reservations for any device necessary.

And to answer you question: DNS is for name resolving. So in any case of name resolving you need a DNS server.

What is the use of setting a fixed IP address to an accesspoint? I prefer to have all my IP related stuff done by a DHCP server, reservations for any device necessary.

This approach is fine until your router bites the dust and you don't have a backup config saved with the reservations in it.

Both methods can work. Depending on the policy or preference, some company prefer fixed IP to dynamic IP. I believe that the control for fixed is much easier. However it requires more settings. If we use the DHCP client method, the connected device can receive not only IP but also dns server and gateway.

YH