The rule of 7% is more potent and easier to understand.
It tells you that if market grows by 7% annually, it's going to move more volume in ten years than in all years before, combined.
For example, of country's electricity consumption grows by 7% YoY, it's going to consume more electricity in (any) ten years than it ever consumed before that, grand total.
I fail to see how you can compare the two rules of thumb. For starters, the rule of 72 is simply talking about doubling (not about aggregate consumption)and the rule of 72 isn't fixed to a single interest rate (7%).
It tells you that if market grows by 7% annually, it's going to move more volume in ten years than in all years before, combined.
For example, of country's electricity consumption grows by 7% YoY, it's going to consume more electricity in (any) ten years than it ever consumed before that, grand total.