I just finished a Cisco CCNA video course, so I know just enough about networking to be dangerous. I have a pretty good idea of how IP's and subnets work, but one thing I haven't been able to find out is why, exactly, 255.255.255.0 is the default subnet mask in most of the routers I've seen (admittedly, nearly all consumer-grade and SOHO routers).
Granted, there's not all that much of a reason for a consumer-grade router to use anything else - unless you need more than 254 IP's, or want to do something complex like organizing your network (servers on 192.168.1.X, desktops on 192.168.2.x, etc.)
That got me thinking, are those the only reasons to use 255.255.255.0? What exactly would change for people if the default mask was 255.255.0.0 instead? Is there some downside to using the latter?