The 'rule of 72' is a quick and easy rule of thumb to determine how long an investment doubles, and improve how you think about compound interest. For example it takes approx. 10 years to double an investment at 7%, or 7 years at 10%.
That's a pretty hefty fee when you compare relative to average annual returns. Plus the compounding nature of those costs is not insignificant. Jack Bogle (Vanguard) has a nice chapter demonstrating this in "The Little Book of Common Sense Investing".