[jpeterson]

Investment markets operate on relative gain, not absolute gain. E.g.: if you invest in a stock and it gains $5, this would be a great return for a $1 stock but a poor one for a $1000 stock, so the absolute gain doesn't mean anything on its own. A 5% return always means that you've gained 5% on your investment.

[ak39]

Would it be the same (valid) with percentage returns?

[goodside]

Less so. Log-normal returns are better because they have the property that a summation of log-normal returns over contiguous intervals is equal to the log-normal returns of the combined interval. In other words: Losing 5% and then gaining 5% doesn’t put you back at exactly 100%, and log-normal fixes that.