Carbon use is purely personal choice. I only use it in my fry tanks, it keeps the water nice and sweet for the growing fry. I dont use it in the others because most are planted and the plants filter out any nasties that maybe there. I buy carbon in loose form and bag it myself to fit any filter i may need it in at the time.
Carbon though is only effective for around 4 weeks, many do not realise it loses its ability to remove nasties after that time period. Due to this many think its no good to use it. Using carbon is just another way of keeping your tank sweet, but like everything maintenance needs to be done.
If you have a tank that smells, i would not be using carbon to remove it, i'd be seriously looking at what is causing the smell problem. None of my tanks smell in any way, and a well maintained, properly cycled tank should in no way smell, in fact even my new non cycled tanks (but well maintained) tanks do not smell in any way. If a tank smells, something is wrong.