So obviously if an item has a large margin its going to be good to flip but in terms of gp/hour it can be more efficient to use a smaller margin. For example if I buy 1000 of a for 90 and sell them for 110. This round trip takes 10 minutes to complete and gains 20k. But, if I buy 1000 of a for 93 and sell them for 107, the round trip may only take 5 minutes, gaining 14k. This is obviously less money gained but it was done in half the time. So, with the 5 minutes that was saved a similar flip can be done, say earning another 10k. This means that in the 10 mins, 24k was made instead of the 20k from the greater margins. This is only really useful when you have a smaller cash stack and need the flips quickly to make money or you have run out of slots in the GE.