I use a chart as well, just to know if we are in a middle of a range. Usually I am trying to follow the big money and get to "thick" areas. if they pull their orders at those areas, great, I caught a big move and will ride it as long as I can.
To get an idea of how likely you are to get filled... If you're trying to sell on the offer but will pay up if necessary and the bid is obviously not going to last much longer, then you want to know if your offer has much chance of trading...