We used to have DHCP based jails. The problem is that every time they start they got a different MAC address. If you run DHCP this is a fail because you can never guess what the MAC address would be, so each time you start a jail you get a new IP. For jails that require port forwarding from your firewall (like Plex) this makes them utterly useless as the IP is always changing.
Also for anyone that actually wants to access the
http://jail.ip/something you have to constantly keep track of which jail is which as they are always changing.
For reasons I didn't understand and still don't, every time you start a jail you had/have no choice on what MAC to set. So you got what you got, which made them useless.
The solution... go to static IPs. Then you can be sure that your plex server is always .100, your mumble server is .101, etc.
Now we're either taking a step backwards or something has changed and now we can do DHCP with static MAC addresses. :p
All of my jails *depend* on having a static IP. I can set it via DHCP or via static ip in FreeNAS WebGUI, but if it's going to be an always-changing revolving door I can go ahead and shutdown my jails now because they will be useless to me in 9.3.