For backpacking use a cot would have to be awfully light, say a pound or two or so before you could seriously consider taking one along on your back on a pack-in of any consequence.
However, here in the NW it can rain ... to the point where you will have water creeping into your teepee despite careful siting and your best water diversion efforts. Last years elk hunt in WA was a case in point. Without a cot in my 8 man Kifaru, I would have been sleeping in a small lake. A cot allowed me to sleep dry during the worst of a multi day deluge. In this case though, I was camping out of my truck & could afford the weight of a light cot. There are times when staying dry in a floorless tent or even a well built tent with floor and additional groundcloth can be a real challenge.
I don't use one backpacking but for use out of a vehicle, a light, compact cot can be a real treat.
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