Living a global economy means not only that companies have to compete with more and more competition, it also means being available to clients 24 hours a day, since a client might be in a country which is in a completely different time zone.
Even if you only sell at a national level, having a site that lets clients purchase from you without waiting on the phone is becoming the norm in every industries. By automating repetitive purchasing processes that are the same over and over, you can liberate your staff in order to take care of exceptions and special orders where human decisions have to be made.