As each host has to be registered in the DHCP server with its MAC address and authorized in some group at the border firewall, we can define which area does it belong to. Of course, this is only for simple management purposes. When you are limited to a single collision domain without a real network control architecture (VLANs, Radius server, Authentication, etc), you cannot really enforce the IP usage. Any tech savvy user can reuse an IP of his/her area to statically connect any computer. But in the use case this solved the user needs with the available budget and tech support personnel.

I have some student labs to manage in addition to the admins, utility and teacher rooms managed with DHCP giving fixed addresses. I assigned a single private /24 range for the labs but subnetted it in /27 chunks of 30 hosts to identify each one. That way I have the capability to give distinct Internet access rules for each and also can find where are the problematic pcs when an issue is detected. When we grew over the eight /27 spaces available, I increased the main range to a /23 and got another eight labs (I had left space to grow, we never know if there is a future need ;^) ).

@Milind R The IP ranges are separated by virtue of its mask. They can coexist in a single Ethernet domain, but share the media. There is no rule enforcing for it, save the administrative hassle, but that could be useful when you want to limit the IP broadcasting of certain noisy protocols between small areas or laboratories or not have administrable switches capable of VLAN partitioning.