I usually use one, the left. I have spinal problems that makes my right side weaker and have less stamina than the left. I'm also fairly plump, picture the Pillsbury Dough Boy or the Michelin Man trying to get both fat legs under the table. So I use the left foot mostly. I do try to use both occasionally, but the left leg is dominant and the right leg fatigues faster, so the left is doing all the work anyway, so I just use one.
Joe