It does have some very valid uses in the aquarium however k1w1y2k, so I would do some research on it and decide what you might want/need it for.
The following paragraphs will give you an idea of what you need to consider;-
"There are conflicting theories arising from the use of activated charcoal in an aquarium. Firstly, some people believe that it should be used permanently. The second school of thought promotes the occasional use of carbon. Personally, I believe that generally it is unnecessary to use filtration over activated carbon continuously. It is best used in response to particular requirements, such as the elimination of toxins, medicinal residue, or pigments such as tannin (given off by wood or peat).
Filtration over activated carbon can prove useful in the long term to treat water containing high concentrations of undesirable substances like chlorine, chloramines, alum, phenols and insecticides and pesticides. Reverse osmosis systems are usefully coupled with activated carbon pre-filters. Used in conjunction, they eliminate chlorinated by-products than can damage the membrane. However, they are not very effective in the removal of nitrogenous by-products. Only the rigorous upkeep of biological filters and efficient biological filtration can help eliminate ammonia, nitrite and nitrate.
The Negative Impact of Activated Carbon
Activated carbon can be criticized for its inability to differentiate between “good” and “bad” molecules. It also fails to retain important trace minerals, including those needed by many hard water fish species and many plants. In reality, the adsorption power of activated carbon is dependent upon the different parameters (e.g. pH of the water) or the chemical form under which the element in question is found. The power of adsorption is limited and it losses its fixation capacity after several days, once it has become saturated. Even worse, it can then release the molecules it had previously extracted back into the water. Therefore, it must be replaced frequently; frequency being dependent on the saturation or concentration level of undesirable elements in the aquarium."
..... credit for the above goes to a cichlid site in aussie 'wessterncichlids.com.au'