If you're like me, your home network is a bit more complicated than just providing Internet access to a laptop and a few mobile devices.
My network, for example, has two desktop computers, five laptops, three tablets, four phones, a Raspberry Pi, an iPod Touch, two Kindle book readers, a printer, a smart TV, a DVR, three game consoles, an Apple TV and an Internet-connected Hi-Fi amplifier. That's 26 devices and I haven't even mentioned the cable modem, the router or any of my older devices that are rarely turned on.
Additionally, although most devices access Internet services, many of these devices access each other. For instance, the two desktop computers are running servers for web pages, file sharing, music sharing and remote login.
When you've got a network this big, the factory default configuration that comes with your router, whether purchased or provided by your ISP, just isn't going to cut it.