Nitpicking: in modern car gearboxes the actual gears (cogs) are always engaged, and the grinding noise is made by parts that are sort of designed to take it. I

Nitpicking: in modern car gearboxes the actual gears (cogs) are always engaged, and the grinding noise is made by parts that are sort of designed to take it. If you grind them a lot they'll still fail, but until they do there's no degradation to the way the gears mesh and transfer power.