All Ordinaries

Almost all stocks have positive correlations for the general market. When the market goes up, they rise. When the market goes down, they go down. Some more than others. The beta of a share is a measure of correlation. High beta stocks rise and fall more than the market overall.

So if the market is generally rising, then chances are very good that a particular stock will follow the trend and vice versa

It is only important if you have a portfolio of actions large and diverse as all the major pension institutions must do so. The index indicates VALUS General sharemarket total. If you invest in only a few stocks, the index does not make sense.