Purpose of Decanters?

I can't imagine that there is any advantage to decanting distilled spirits. With scotch, you want to minimize exposure to air (oxygen); some people even inject nitrogen to displace the oxygen in order to reduce exposure once a bottle is opened. Decanters are strictly for appearances when it comes to distilled stuff. For wine, they are used to aerate the wine for an hour or so prior to serving.

To pour older wines off of any sediment in the bottle and to give younger wines a vigorous aeration to help them open up.

A captain's decanters design lowers the center of gravity so that it is less likely to spill during rough seas. It has been romoured that alcohol can leach the leach lead out of some old lead crystal decanters. Some decanters meant for spirits can be very generous to angels due to their less than air tight stoppers.

Kind of an odd topic for A'gon. I am not sure why any scotch would require a decanter. Decanting wine or port serves two purposes. First, if there is sediment in the bottle, decanting separates the liquid from the sediment so one is not drinking sediment. Second, decanting hastens the breathing process by virtue of the physical act of pouring the liquid into the decanter. Also, wine will tend to breathe more quickly in a decanter as most decanters are designed in a shape that allows the wine to be exposed to more air than if it was left in the bottle.

A decanter also allows one to judge the color before the wine is in the glass.