Generally PC's are fine to setup using DHCP. Other devices, as mentioned before, printers, web cams, anything you will connect to via IP address need a static IP. If DHCP were to change their address, none of the PC's would be able to connect to them anymore via their already set address.
An exception to the PC's using DHCP is servers. You want to statically assign a server IP address because again, PC's will be connecting to it.