butch ... pinning the lug just makes sure that when you remove the barrel and lug to put a new tube on, the lug ends up in exactly the same position relative to the action as it was when the original barrel was installed.
If the recoil lug is not in the same position for the new barrel - and if the bedding for the lug is very tight (as it should be), the lug will dictate how the action sits in the stock. If that happens, the action can be canted when set back in the stock. Now, when you go to torque the action screws down, you are creating stress between the action and the recoil lug, which may result in problems.
Only if the guy putting the barrel on don't know what he's doing.
