More importantly you keep the portfolio semi-balanced.
Just using Google / Gold as a comparison [1].
Assume you have 100 units of each.
In late 2021, Googs gone up ~100% so you have to rebalance because you have $200 in Goog and $92 in Gold. So lets say you rebalance to 80 Goog (160$) and 144 Gold ($130).
In late 2022, Googs gone down ~40% so you have to rebalance because you have $96 in Goog and $141 in Gold. So lets say you rebalance to 100 Goog ($120) and 118 Gold ($112).
So over the course of 2 years Goog has gone up 20% and Golds gown down 5% but your investments are overall up 16%. Obviously a 100% Goog investment is higher but with more risk.
If you didn't do any rebalancing then you have a gain of 7.5% (100*1.2 + 100*0.95 = 215)
More importantly you keep the portfolio semi-balanced.
Just using Google / Gold as a comparison [1].
Assume you have 100 units of each.
In late 2021, Googs gone up ~100% so you have to rebalance because you have $200 in Goog and $92 in Gold. So lets say you rebalance to 80 Goog (160$) and 144 Gold ($130).
In late 2022, Googs gone down ~40% so you have to rebalance because you have $96 in Goog and $141 in Gold. So lets say you rebalance to 100 Goog ($120) and 118 Gold ($112).
So over the course of 2 years Goog has gone up 20% and Golds gown down 5% but your investments are overall up 16%. Obviously a 100% Goog investment is higher but with more risk.
If you didn't do any rebalancing then you have a gain of 7.5% (100*1.2 + 100*0.95 = 215)
[1]: https://www.google.com/finance/beta/quote/PHYS:TSE?compariso...