Not convinced its a must have, but definitely its a doesn't hurt to have piece of kit.
I'm still not sure about the "must have" need of a footprint but this footprints material was much more robust than that of the bottom of my UL 2 and was of very high quality. I can see that it would increase the longevity of your kit and maybe even resale-ability if used every time you pitch.
The plus's for me are if you find yourself needing to pitch on less even rockier ground, this would reduce possible damage or if you're on a multi day trail and want a quick pack up of your tent without packing with the ground sheet still wet this is a lightweight useful option to your kit. These were the reasons I bought it.
Its super light and as its a separate piece of kit you have the option of adding that weight or not. Overall I think its been a worthy purchase but not sure its a must have at this stage. It would be a personal choice depending on the type of tramper you are.