The licenses operate just as you'd expect. You license the services as perpetual so they never expire or as an annual subscription license which operates from 1-5 years. If you go with subscription-based license, the services die when the license expires.
One benefit can be in upgrades. Certain models, like 2215 can be upgraded to 2225 via a license change. If you subscribe to 2215 and later need to bump up to 2225, you can upgrade the existing license.
So far, none of what I have discussed covers the hardare. Above could be hosted virtually at no additional hardware cost. If you want an Infoblox appliance, you would have to add the "shell" appliance cost and maintenance.
One benefit most do not use is that perpetual license can be moved from one appliance to another. If you have a 2210 today, you can replace the hardware (as 2210 is end of support in 2020 or 2021) with the new 2215, but only pay for hardware and move your existing perpetual license... I've never done this, but this is what I've been told.
