retraining Highland Clansmen? What is the point?

[Stazi]

Thanks for the extra info. So if a commander's unit is worn down to just a few men, or just the commander himself, when that unit is retrained the valor V&V would only apply to the original survivors of the time the V&V was first applied?

It works not only with decimated units. For example - you recruit new unit with 3 valour. Next turn commander gets a nasty vice that gives -2 valour so now unit has 1 valour. You put unit for retrain and... next turn you get unit with 3 valour again. The unit's commander still has the vice but it looks like it doesn't affect the unit.