Aquarists who have learned husbandry information supplied by store employees and manufacturers are often surprised that many of the products that they are sold are either unnecessary or ineffective. Many additives are genuinely important to aquarists (many calcium and alkalinity additives, for example).   

"There is a dark side to the hobby, with manufacturers pushing products that have no useful purpose. Aquarists should be skeptical of the claims of products, especially any that seem too good to be true. They probably are." -- Randy Holmes-Farley.