Besides being a hiker and backpacker, I'm a canoe tripper. I've not only done trips down rivers in the West, I've done several trips in the Boundary Waters. There is a well known Boundary Waters canoe camping guru named Cliff Jacobson. He says that the ground cloth should go inside the tent for two reasons.
1-most of the wear occurs on the inside, not the outside.
2-any water from a leaking floor or condensation will stay under the plastic, keeping your sleeping bag dryer (Drier?).
Someone asked Backpacker magazine about this and the guy that responded seemed to think it was just about the dumbest thing he'd ever heard. There were two basic points to his argument.
1-he's worried about punctures coming from the outside, not inside.
2-if there is water in your tent, the tent is either defective or damaged.
Welcome to the real world. I've woken to water in my tent. Hard to say where it came from. I've been on group canoe and backpacking trips where other campers had problems with water in their tents. It does happen, and if it does, you will stay dryer (Drier?) if you have a sheet of plastic inside your tent.
I agree about punctures coming from the outside, but the waterproofing is on the inside of the tent and easily worn through. If you have a lot of mosquito netting, condensation probably isn't a problem, so I'd take a look at the design of your tent.
If you are going camping and anticipate some serious rain or cold temperatures with high humidity, the safest thing to do, in my view, is use a footprint and also put a plastic sheet, cut slightly smaller that the floor, inside the tent.