There is still question about size mattering, whether light and rigid is as good as heavy and rigid. (I'm thinking of tripods - you think for yourselves.)
Mass is sometimes better able to protect from vibration and breeze. Personally speaking, as amateur, I find that a light tripod - with two legs extended, offers me all the support I need in order to frame with a long lens; try framing, without support, with a 500 reflex. Two legs give enough stability in a chosen plane - usually the horizontal - and tilting the whole enchilada up or down is easy when no third leg to adjust. Of course, I still go for fast shutter speeds where I can, and as I like fairly open apertures at the moment (when not in block mode) that comes naturally.
With a monopod, the only thing you can really depend upon is that you won't reach the centre of the Earth.