Hi,
I agree with Viktor. The empirical data he presents should give us loads of confidence. One of the reasons we get confused (and often perceive information from different sources as being conflicting) is because we fail to remember our objectives in relation to a products performance.
The fundamental operating principle of activated carbon is that it provides a high surface area (on par with the better sintered glass filter media) upon which certain compounds adhere, due to what can be loosely described as a weak electrostatic attraction (Van Der Waals forces). One can think of this in the same way we would pass a comb through our hair and then use the comb to pick up small bits of paper. This attraction is referred to as "adsorption" (as opposed to "absorption"). The expression "activated" sounds sexy but all it means is that the carbon material is made more porous in order to increase the surface area.
Activated carbon does not "choose" which atoms or molecules to remove from the water. It just so happens that many compounds that WE consider bad, for example those that contribute to discoloration, or those that have some level of toxicity, because of their chemical structure and arrangement of orbiting electrons, are attracted to the carbon surface and are held on that surface. Different compounds have different strengths of attraction. Some have zero attraction and are therefore not removed from the water column. Some are weakly attracted and so are only partially (or slowly) removed, while others have a strong attraction and are strongly removed. There is some evidence that some ions/compounds we consider to be micronutrients have some attraction to the carbon surface.
One can then remove and discard the carbon, or, if the carbon is in the filter or substrate, nitrifying bacteria, which also colonize the carbon surface, then have access to an all-you-can-eat buffet of compounds sharing that surface.
So in the grand scheme, based on this operating principle, activated carbon is a very good thing as it removes many bad things. The small penalty is that it may remove some good things, but so what? Just add more of those good things and stop worrying. As Viktor points out, his dosing scheme is less intense than EI or PMDD therefore, if no negative results are observed with leaner dosing, then we heavy handed dosers should have little to fear. One simply has to get over the possibility of small losses in micros and carry on. There are a lot more important things that deserve our attention.
To answer the question of whether one "needs" carbon, well, as Chris stated, one can remove bad things from the water column either by doing frequent water changes, or by using alternative chemical filtration such as Purigen. Another way of clarifying the water is to make the bacteria colony more effective by increasing their population though oxygenation and by better distribution of O2 in the water column. This is done by increasing CO2 levels. So you can see that the question of "need" depends on what path is to be followed and what the hobbyist feels is easier or more appropriate for his/her circumstance. One also has to consider which bad things are in the water supply or are generated by the tank itself along with the assessment of available time and resources when deciding the method to use.
Cheers,