I like the idea of fighting on a young Knight/Exodites planet, I've loved that lore since Epic Space Marine and fighting a campaign there would be cool. The sustainability of agriculture and livestock on these worlds is key to their importance. Not sure that a Guard Regiment would be wasted on digging anything that wasn't a trench, but I could see them fighting on these types of worlds. Helping establish and protect colonies and secure large areas would be the key goal, after that I suspect there would be a lot of scouting and skirmishing. I've always envisaged these worlds to be sparsely populated so the Regiment would probably have quite a bit of ground to cover. Once the major threats had been dealt with and some decent PDFs had been raised I think the Regiment would be lifted out of their quite quickly, assuming the Departmento Munitorum didn't forget about them.
As for worrying about agricultural output, that's not really a Guardsman's remit until his Regiment gets disbanded and left to found its own home.