Rockwool is a very popular growing medium because it is premade for use with indoor hydroponic systems. It eliminates the need for transplanting. Simply place the existing cube on top of a larger cube and the plant's roots will grow through both cubes. Rockwool holds 10 times as much water as soil, but its porous nature makes it impossible to overwater. It can also be rinsed out and reused for your next crop, making it both economical and environment-friendly.
Disadvantages of rockwool
Rockwool has a natural alkaline pH, which means it must be pre-treated before using it as a growing medium. One way to pre-treat is to soak the rockwool in a mix of pH Down, trace mineral solution, and fish emulsion for 24 hours, then rinse thoroughly. Rockwool can also be irritating to skin when dry, but usually is not when wet. Always wear gloves when working with rockwool.