How do people know computers are useful? How do people know you can buy one and what it costs? How do people know where to go when they want a computer? Without

How do people know computers are useful? How do people know you can buy one and what it costs? How do people know where to go when they want a computer? Without advertising there is only word of mouth, which is slow and probably doesn't reach many people at all. So if computers are useful, shouldn't it be allowed to advertise them?