I'm with Steve on a few of these points. In addition, running Carbon 24/7 while not really neccessary, it's sort of like us being able to live in a house with free floating polutants - yeah we can live there but not very well
I differ on my choice though. I use Seachem's Matrix Carbon - they have the best claims anyway and they are a very reliable mfg and do test their products very thouroughly and I also like the spherical approach to filter media - it definately provides hugh surface areas and excellent waterflow. In fact when I rinse my Purigen (same basic shape as Matrix carbon) it's wild to watch. As soon as the water hits the filter bag containing the macro-pellets it expands to twice its size absorbing the water like crazy yet not impacting its flow through the media.
I have run tanks for long periods of time w/o any Carbon - but I typically do not do this anymore. Why - Cuz many checmical pollutants that could enter the water in a variety of ways may not kill your reluctant charges but may make them a bit less healthy and Carbon is a good way of riding the water of these provided you use it deligently.
Just my thoughts on this.