The conventional view of portfolio rebalancing is that it is a strategy to enhance long-term returns by periodically selling the investments that are up (and overweighted) to buy those that are down (and underweighted), in the process of realigning the portfolio to its original target allocation.
Yet the reality is that because most investments go up far more often than they go down, systematic rebalancing is actually more likely to just consistently liquidate the best-performing investments to buy ones with lower returns instead – especially when rebalancing across investments that have very significant return differences in the first place (e.g., rebalancing from stocks into bonds).
As a result, rebalancing may be helpful as a risk management strategy – otherwise higher-returning stocks would compound to the point that they are significantly overweighted relative to lower-returning bonds – but it’s only when rebalancing amongst investments with similar returns in the first place that rebalancing provides a return-enhancement potential.
Ultimately, the fact that rebalancing may actually reduce long-term returns isn’t a reason to avoid it (even if returns are lower, risk-adjusted returns may be improved if the risk is reduced by even more), and sometimes returns really can be enhanced (when rebalancing across similar-return investments, such as amongst sub-categories of equities). Nonetheless, it’s crucial to recognize the role that rebalancing really does – and does not – play in a long-term portfolio!