It depends on your situation,
To have a DHCP server for each network subnet individually is not a scalable solution, as you may need to work a lot when configuring and maintaining it.
To have 1 DHCP server for the whole network is comfortable, as you need to modify the configuration in one server only, but this is a single point of failure.
Probably a good solution would be to have 2 to 3 DHCP servers located at different points of the network.
The number is not so high that you cannot handle, but in case of failure of one of the servers you have redundancy.
But in this case you will have to take care of configuring the ip helper-address commands in the routers so the clients can access the DHCP services through the network.
Cheers:
Istvan
