good question but i am not bothered with taking time to answer or even in trying to find the answer:because i get my profit and loss, by price.
volume supposedly leads price and this may be true but unless you know and can measure exactly by how much, volume leads price, it is of no use to me: "if you cant measure it,you cannot manage it"-Ed Seykota
The profit and loss may come from the price, but typically the buy and sell signals come from technical indicators. I have found volume useful since approximately 70% of my technical indicators are based on volume.
Ed's quote "if you cant measure it,you cannot manage it"
Mr. TNA's quote "if you don't know how to measure it,you cannot manage it"