I cringe everytime someone mentions seriously "pulling up" on the pedal with clipless setup. I mean yes you can pull up but I wouldnt recommend this, unless you feel you have no other option. Holy stress on the knees batman!!!!! The "drag back" is more plausible with clipless pedals.
As far as the benefit....I feel more balanced and in control. Also your feet stay in one place, no slipping or sliding, especially with rain or any type of weather. In terms of power, it is my understanding, that it more or less sets the bar even, in that the amount of gain you obtain from using the extra motions allowed by clipless pedal systems, is still negated by the loss of power transfer in your drive train...lol. So riding without the clipless, especially for long distances, you would theoretically be using more effort overall.
Cheers,