reasons NOT to bother with a power meter
you hate technology
you are lazy and inconsistent with your training
you are unwilling or unable to suffer
you do not have a coach AND you have no desire to study anatomy, physiology and biomechanics
you do not own and/or cannot operate a PC
you are too uncoordinated to operate the on bike computer without crashing
you just ride a bike for fun, fitness, and fashion and do not wish to test your physical and mental limits
you just like throwing money at your bike...
(in which case you would be better to buy a $2000 wheel set and a $20 cycle computer)
you are unable to follow a structured and scientifically controlled training program
you can't handle the truth
you are afraid to ride like a savage