Just because the gears overlap does not mean you don't use them. Obviously your cadence is higher in a smaller chain ring than a bigger chain ring. Sometimes you want to emphasize your heart with a higher cadence or other times your muscles with a lower cadence. It is just being aware of your choices and how much to double shift when you switch chain rings.

On my triple when I am using the granny or biggest chain ring I usually don't use the two most extreme cassette gears. This is mainly to avoid the noise from cross chainining and also the wear that can be caused even though the wear factor really is not much of an issue with modern drive trains. I only use the middle six gears on the cassette when using the middle chain ring. So out of 30 gears I avoid using 8. If it were a 20-speed I would avoid using 4.