I have always removed the liner as a matter of routine while cleaning, just as I remove the nipple on my percussions. It's my feeling that some fouling may collect if there are any nooks and crannies inside the barrel where these are installed. Also, on my half stocks, the larger hole aids in the pumping of water thru the barrel; my full stocks use a tube with a fitting that screws in the vent hole to allow water to be pumped thru the bore. I've been doing this for over 30 years with muzzleloaders with no ill effects. Never thought of it as anything but the standard procedure until read of some folks leaving it in on this forum.