Yes...a DHCP reservation is different from static.
DHCP works in scopes. For example, you can assign a scope that says "hand out any IP address between 10.0.0.2-10.0.0.254" and it will give out any IP address in that range (more or less at random but there's more to it than that).
DHCP reservations are set using MAC addresses and basically pair an IP to a specific MAC address. So, you say MAC "A" gets IP "A" and so on. The IP address is still given by the DHCP server, but it will, ideally, always give the same IP for that particular device.
Static IP addresses do not have DHCP involved. This is the process of manually configuring, at a minimum, the IP address and subnet mask directly on the device. Since the DHCP server (typically the router for most home setups) isn't involved in this process, it won't automatically know the IP address selected is in-use.
Static IP reservations in your DHCP server are to account for the bullet above. This is how you can use DHCP for some devices and static setup on other devices without having to worry about the same IP address being given to two different devices. This configuration tells the DHCP server to not assign the IPs added into the static reservation list. More often than not, with modern networks, static assignments aren't needed (and are generally not recommended) for user devices.
A real world example (glazing over a lot of the technical details):
You have two PCs. One is a laptop where you don't care about the IP address. The other is a server that needs to always have the same IP address. Then you have a really old network printer that can't do DHCP.
- Your home network is 192.168.1.1-192.168.1.254.
- 192.168.1.1 is the IP address of your router
- You set a static reservation list of 192.168.1.2 (the DHCP server will never assign these IP addresses and will not know what devices are using them). You then go to the printer and put in this IP address as static.
- You give a DHCP reservation to your server at 192.168.1.3 (the server will always get this IP address and the assignment will show up in your DHCP usage list).
- That will leave 192.168.1.4-192.168.1.254 to be assigned to the rest of the devices by DHCP (the server will pick an IP address from this pool to give to devices and will keep track of them). The IP address for a particular device may change at random.
The general recommendation for Hubitat is to do a DHCP reservation for the hub in your router's configuration and leave the hub set to DHCP.
