That is the stat for how many turns it takes to build a unit in a settlement. This is found in export_descr_units.txt, in DLV's '\data' folder.
The downside to having a value higher than 1 is that the player will retrain units but the usually AI will not.
It will take longer for the AI to recover from a nearly destroyed army than the player.
The value for how long it takes for a recruit pool to recharge (which makes a unit become available to build) is in export_descr_buildings.txt.
For each building that can produce troops you will find a line like below for every troop it can produce and at each level of the building.
recruit_pool "Ducal Sword Infantry" 0
0.5 4 0 requires factions { lit, } and region_religion pagan 60
The lower you make that
bold number the longer it will take for troops to become available. I think It will accept 3 or more digits so you can have '0.01', for example, greatly reducing the amount of that troop type in your games. You could also add another line just for retraining like so:
recruit_pool "Ducal Sword Infantry" 0 0.01 4 0 requires factions { lit, } and region_religion pagan 60
recruit_pool "Ducal Sword Infantry" 0
0.8 0.98 0 requires factions { lit, } and region_religion pagan 60
Here the second line allows a faster buildup (0.8) which never results in a full unit (0.98). So new units will only rarely be available but you will always be able to retrain your 'rare' units as long as they are not more than 98% destroyed.
But, like I said, the AI will not usually retrain units so the benefit of an extra line for training will only be felt by the player.
edit: Oops I really should have mentioned that TWCenter has a great forum for questions like this:
http://www.twcenter.net/forums/forumdisplay.php?f=276
You can also search for a tutorial on
EDB and
EDU and usually you'll find something nice

(stuff for RTW usually still applies to M2TW)