There are lot s of dhcp server, but we talk about ISC-DHCP.
When you start your computer, the network interface bring up and query an ip to the DHCP server. Without it, you must specify each time your network address, and it will be very annoying to communicate with your computer. Your IP, and your DNS name is unknown for everybody.
But with DHCP server, you can get a valid IP and a DNS name, but also a ntp config or nis config or more (cf rfc2132)
We will work with include sub command and many config files, it will be easier to understand what we need and the difference between all configurations.
The config files have many parts.
Like DNS, and even more, we need a secondary DHCP server. In fact, without DNS we can use network, it s hard but we can. without DHCP and if we don't know the topology network, it's impossible to use a network computer.
Because DHCP give you ip (and more) parameters, is will be less difficult to act as multiple server. You computer send a broadcast and all servers can give an answer, the first will be notify and managing it. We can see here that DHCP server must know and share all knowledge in real time, and of course must have the exact same config.