The fact that they have a large grass patch for farming is the main usefulness or practical benefit. Some have more grass than others. Some have more rooms than others for storing furniture.
Also, there's some kind of tower rush technique that can be executed when you invite your guild members to the guild house and then kick them all at once...
What else to use it for? Hosting parties or games... pretty much anything you could use a house for, actually... cept it's bigger.