An all in one PC is an all in one computer that runs Microsoft's Windows operating system (for example, Apple's iMac is an all-in-one solution as well, but it utilizes Apple's proprietary OS, so is not typically considered a "PC" even though it is still a personal computer). For individuals who are accustomed to Windows, and who are seeking a compact and intuitive system that is easy to set up and use, an all in one PC is the obvious solution.
For the average consumer, an all in one computer will be the ideal choice, and that is because they are truly "turn key" solutions. You do not have to purchase a display monitor, keyboard, and mouse separately; you do not have to worry about syncing your tower with the various accessories; and you do not have to worry about finding real estate at your desk for the various components. All in one computers are smartly packaged, beautifully designed, comprehensive solutions that pair the power of desktop computers with the usability of laptops. For the average consumer, an all in one (or AIO) is often a better solution than a traditional tower computer, due to its ease of use.