I am in the middle of building my home and garage.
When I was deciding on my house plans we decided to also put plans for a garage in and build along with house.
My architect charged me for plans for garage and it was only after the plans went into the council that I seen on council website that you don't need planning permission to build a "domestic" garage.
Of course my arctitect did'nt tell me this becasue he got paid for the garage plans.
We did'nt really need plans for a garage as it's not rocket science in building a garage!!
I think that there may be an advantage to having received the planning permission as it forms part of your exempted developement if you do not.
You now have that exemption intact so you can put up other things later.
I may be wrong on this but that is my reading of it.