"Why is equal gearing so important?"

Its not for most folks. Andrew is correct in post #2 . a 10 - 15% range is fine. Low gears can even go to a 20% jump. Higher gears I'd try to keep closer to 10%. I often use the 21% drop between my 48 and 38 chainring climbing hills or approaching an intersection where I don't want to linger in traffic.

If you are on a professional racing team and that last 1- 2% efficiency means the difference between 2'nd and 6'th place, Or being kicked off the team, Then yes, Its important.