Legally it's an option rather than required, enabling building regs process to be quicker. The alternative is the LA having to actually assess and inspect the calculations.
But I guess the grant awarding people add it in as a gold plating to make life simpler and easier for themselves.
I'm surprised Farmplus hadn't heard of it as even non grant funded people might go that route quite a lot, you would think, maybe they are used to doing mainly smaller buildings which are funded by the farms /smallholders wholly?