wot does it actually do

allows you to put low level troops from the barracks straight into high level troops standing on the barracks

Troop level is useful in situations where you expect to do a lot of damage. This is because in regular campaigns, (not skirmishes) there is a limit to the amount of attack damage you can do, the limit is 1000 points of damage in an attack. If your attack is 1000 or over, you only get 1000 points damage. Each additional level adds a possible 10 points of damage to that limit. Therefore, a level ten troop will do 1000 + (10 X 10 = 100) = 1100 points of damage.

There is no limit on retaliation. You could do 1000 points of damage and receive even more damage yourself in retaliation. It truly sucks when you attack somebody and lose 100 troops and they lose about 10!

One more thing, when you use advanced recruitment, you pay the higher cost of higher level troops to add to the stack so it can be prohibitively expensive. If you had a level 50 scout, population 2, you might beef him back up to 200 pop, but it would be a ton of gold to do it. This makes this tech one that I think few players use.

LOL. Mog is right! Few players actually use it and I hope it stays that way or I might not be as effective on the battlefield.