With online printable coloring pages you never have to keep volumes of coloring books around. Most children change what they would like to color often. They bounce around from one theme or one set of characters to the next. Therefore they may abandon that coloring book with princesses or cars days after you buy it. Printing out the pages though allows them to always get what they want.
However, it isn't just at home that they come in handy. Many professional offices take care of children. There are also parents that have to bring their children along with them for business. It may not be ideal but they often can't afford child care or it is hard to find someone to watch the youngsters so they can take care of things.