1. Divisible loads
Transport exceeding the usual dimensions of 16.5m (+1.5m overhang) in length, 4m in height, 2.55m in width and 40t of weight obviously needs special permit. These permits are only granted for indivisible loads which means permits wouldn't be granted if the cargo could be transported using normal trailers.
Therefore, the following loads are illegal:
lowbed trailer:
- 2 Loaders
- 2 Semi lowbed trailers
- 2 Tractors + Plough
- 3 Air conditioners

low loader trailer:
- 2 Tractors
- 2 Air conditioners

2. Unnecessarily extended trailers
Most cargoes on extended chassis could be transported on a non-extended chassis just as well and no authority in the world would give a permit for that kind of overlength.
I'm going to show just 2 example images since this unfortunately applies to most cargoes on extended chassis:
