Why clients use a changing IP instead of a MAC address?

[Chris_Anthony]

Trying to understand Clients in groups and why using IP addresses when they can be changed instead of using Mac addresses. Does this mean next time my device gets a new IP address I'll have to add it and to the group I want it in? Or I'll have to set the device with a static IP? (More difficult to do with ipv4). I'm trying to setup a group for my work devices as only they should be white listed for certain VPN services etc.
Pi-Hole 5 is running on a Raspbian GNU/Linux 10 (buster) with DHCP running on a Google Fiber ISP network.
Raspberry Pi 4 2gb

[PromoFaux]

There is an already existing discussion on this topic, with an answer from a developer:

Groups and DHCP

No, the router sends the replies on behalf of your clients in this configuration. There is no possibility for Pi-hole to see who the original requestor was. Hence, they are one and the same client. IP address. DNS queries are asked using either the UDP or TCP protocols. Both use IP addresses for describing the source and destination of the packages. Hence, IP addresses are the only thing visible to the DNS server. We can source hardware addresses (using other means) for devices not more than…