Powdered nutrients are absorbed by plants at the same rate as liquid systems. This is because the powder is mixed with water before applying it to the roots. Liquid nutrients can be anywhere from 20-90% water while powders have essentially none.
Because powders react like liquids, any advantages over liquids are primarily in storage. This means that they take up less space, are easier to handle, and offer higher concentrations or density than liquids. The higher density translates into cost savings during shipping as well as storage.
Shipping cost savings become especially helpful on commercial scales. But even home-grows benefit from the increased portability, especially if they are growing in a closet or spare room. Hydroponic operations might find additional benefit with powders in the form of less sediment in the lines.