Military Units and training (Golden Rainbow)

When dismantling a unit it tells me that "all effort to train the unit will be lost."

What exactly do they mean by that; are soldiers in units for a long time better than soldiers in units that have recently been created?

In the documentation the only thing I read about this is that it uses ammunition for training to keep a "base-level." But says nothing about what effects training has on the soldiers.

It doesn't mean anything right now

Thanks a lot for your help.

Does it cost anything to set one up or can I just create them when needed and dismantle them when needed and not worry about any type of cost in terms of equipment or money?

You can just create them at will for no cost.