Cylinder Drains?

Stumbled across this thread on TT Link about the rebuild of a 4" Foden. At Post #18 someone expressed surprise that drain cocks had been fitted - a feature not present on the 12" version. The next poster expressed the opinion that they were a good thing.

My limited understanding is that the conventional practice is that the drains are opened when first starting to clear any condensation and also when descending a hill,
a. to clear any priming and
b. to limit the pressure in the cylinders if the reverser is used so that compression in the cylinders acts as a retarder.

My questions are:
Have I understood the purpose correctly?
Are there any other reasons for opening the drains?
Is there something about the design of the Foden waggon that makes drains unnecessary?
Would it be a good thing to fit them on the 6" Foden particularly as they are out of sight?
If the answer to the above is positive is the design/manufacturing process for the cylinder block at a stage where the modification could be incorporated?

Martin

drains shouldnt really be opened when going downhill, if the regulator is closed there should be no reason to prime.

Running with the drains open removes all cylinder lubrication and if the hill is a long one, this is a bad thing.

Running the full size roller on the road, i can't say I've used the drains. About the only time they're open is last thing at night and first thing in the morning.