retraining Highland Clansmen? What is the point?

[Stazi]

Retrained units get all bonuses from buildings and province the same way as newly recruited. It especially useful when a unit's commender gets some vices that reduce the unit stats below certain value. For example if you have unit with 3 valour (2 from building and one from province) and the unit's commander gets -2 volour vice, you can retrain the unit and it'll have 3 valour again. Of course if your unit will have 5 valour or more it won't work at all.