This may not fully answer your question but, for the sole purpose of commuting, I could easily limit myself to using only the middle chainring as I find that most of my commuting is done using it plus gears 4-6 on the back. However, my bike is a touring bike and for that reason, I could encounter inclines and declines that would enable me (force me) to use both the small and large chainring and a wider range of gears on the back.