IMO, the advantages of four-down towing are...
- Quicker hookup.
Quicker disconnect.
Don't have to store the dolly.
Don't have to find a place for the dolly at the campground.
Don't have to maintain the dolly brakes (in addition to maintaining the toad's brakes.)
Don't have another pair of tires to maintain/replace.
The disadvantages are...
- Have to install a baseplate on each vehicle that you want to tow.
Some vehicles require modifications (like a driveshaft disconnect) in order to be towed.
Some vehicles cannot be towed four-down.