We have to build thousands of PC's where I work. They are all built with the same image and thus they all use DHCP. A very few of them need a static IP (or at least the owners think they do
). We assign these static IP's but the PC's still use DHCP. We have almost 3,000 PC's but less than 100 of them have static IP addresses.
The usual genuine reason for assigning static IP's is security. My PC has a static IP address and that address is known by various highly secured servers. Thus an ssh from my PC will be accepted.
At home I use static IP addresses because I feel like it. But my roku box must use DHCP, it has no capabilty to enter an IP address directly. This is the only device I know that must use DHCP but I guess that others may exist.