The type of roots that develop in water are different from those that develop in soil or potting mix. If you plan to grow your plants continuously in water, by all means start the cuttings in water. However, if you intend to pot them up in potting soil, use a lightweight soilless mix for starting your cuttings. Some easy-to-root plants such as spider plant (Chlorophytum comosum), Swedish ivy (Plectranthus australis), and coleus (Solenostemon scutellariodes) form roots so readily that you are unlikely to notice any difference using rooting hormone on your cuttings. But most cuttings will produce more roots of higher quality if you dip the basal end of the cutting in rooting hormone. All that is needed is a light dusting. Shake off any excess powder before inserting the cutting into a pencil hole in the rooting medium.