Chart, page-557

Sentiment is what moves any market. A chart (volume included) is just a visual representation of the sentiment/psychology of the participants in that market.Some will argue that fundamentals always drive sentiment,(true at times),but by that premise the Nasdaq was fundamentally worth 5000 points in 1999.
I have a foot in both camps in that I wont buy a stock(or commodity) without liking the FA,but because It's impossible for me to know ALL the information,(or even how much I dont know),using the chart to gauge sentiment,time entry/exit,or decide whether its a short term or long term position,is very useful,IMO.