Electroplating is a process by which ions of a superior metal like chrome or zinc are deposited on a more base metal. The superior metal is dissolved into a solution and an electrical current is run through the mixture so that the superior metal adheres to the baser material in a coat. There are a number of disadvantages to this process, despite how useful it is though.
Electroplating works on a molecular level. As such, when a layer of superior metal is put over the base metal, that coating may be extremely thin. This means that either you have to settle for very thin coats of metal, or you have to put multiple coats onto the base metal. Both of these are major disadvantages of the process, because if you have to repeat it over and over again, it may end up being much more time consuming and expensive than using other methods may have been.
When ions of the superior metal adhere to the base metal it isn't like the coating is being brushed on in a uniform matter. In fact the coatings that you get with electroplating might actually be lumpy and uneven. This means that you'll most often have to grind and machine the parts even after they've been electroplated in the ionic bath. Other methods, such as dipping or spraying, may give you a more uniform coating of superior metal without as much of a need for so much machining afterward.
While electroplating can put a good coating of a superior metal onto a lesser metal using only a current of electricity, that coating may often be brittle and easy to crack. This is especially true with chrome. The superior metal may form microcracks, which can let in impurities and lead to the overall destruction of the electroplated layer. In order to prevent this you may have to electroplate multiple layers of metal on to the base material, but that doesn't guarantee that the layers won't crack and fall apart one at a time from micro stresses.