you know, "rev your engine" e.g. pressing the throtle. The only time it's safe to do so is after the car has been off for 1 minute, and then after started no gears can be enaged (for emission testing, etc.) The manual does not go into detail as to why or say any of that stuff, it just says not to do it. And unless you want to replace your "A" clutch pack, don't do it. Some car might have had a modification such as a hole drilled in the A clutch pack to relieve the presure build up that happens when in park, neutral or reverse. (applies to ZF 4 Hp 22 transmission, but only when mounted to a BMW)
also on a side note: everyone should use or at least try "Amsoil" brand synthetic oil. It out preforms Mobile 1 in every test, by a lot. Look it up, buy it, support it. I'll never use anything else again, what a difference.