Leg room is too precious to put anything under your seat.
...So is it worth not bringing so much crap with you? That's the question people need to be forced to ask themselves.
It's worth not bringing much on the plane with me but I don't see how that reduces the amount of stuff I travel with overall.
I could give 2 ####s how much stuff people travel with overall...what I hate is that in an effort to save money by not checking bags, people make already cramped quarters even more cramped, and inconsiderately take more than their share of overhead bin space. Ultimately, it's the airline's fault for all these BS baggage "fees," but the result is, for me, what has made flying so horrible.
Oh, you want to PICK your seats so you can sit next to your wife? Sure, for $35 extra. Want to take a bag? That's $25. Would you like a snack? $13. Did we mention that you can board early, watch new release movies, AND surf the web? ...For $25, $15, and $13 respectively!
I'd much rather flying just go back to how it was before, when a ticket cost more, but included all the amenities.