For all those who don't think a longsword lightsaber would be practical.
The vanilla lightsaber by itself is impractical for normal people to use and is actually stated repeatedly in Star Wars mythos. So, having said that, having a crossguard is very useful to a jedi/sith for all the reasons having a crossguard on a normal plain jane longsword is useful. No, they won't be cutting their hands and fingers off because if they did, they wouldn't be force users and, as such, shouldn't be anywhere near lightsaber combat. So there you go.
