Prices tell you in which direction an investment is moving, but volume can tell you what kind of support is influencing the price. For instance, if you see a price rise accompanied by high volume, then you know that there are a lot of traders who have confidence in this investment. Seeing this support may give you confidence too. On the other hand, if you see the price of a share of CFD rise on low volume, you know that there are only a few investors pushing the price. This may discourage you from buying yourself.