Originally Posted by Mambo Dave
Yes, there is a minor penalty for "dropping" perks, but it's really pretty small in the scheme of things considering you can have an important crew member right at 100% when starting to grind a new tank, and considering that he picks up training his perks right away upon using the new tank since he is at 100%.
Keep in mind that the perks xp is one big pool...if you decide to reset perks when you have the first one to 100% and the second one up to 50%, and you only spend silver on the reset, you're going to take a 10% hit on the entire perk points pool, not just the points applied to the second perk. They only valid time to use the skill points reset to get a crewman to 100% on a new tank is early in the first perk. Above that, the points hit gets too big.