Rebalancing within the equity classes will incrementally enhance performance over the longterm by enforcing a discipline of selling high and buying low as performance between the various classes varies.
These folks may decide to include asset classes that have no real long-term return with the hope that low correlation with other investment will generate enough excess return from rebalancing to make up for the shortfall.
The long-term trend of the market is up, and as long as you hold true to your strategy and are appropriately diversified across and within asset classes, your portfolio will experience long-term growth.