Well, mostly useless.
If your monitor was higher than it was wide, perhaps people would use it.
But, this sort of feature has been in editors for years.
The thing that would make most sense - especially with current day widescreen monitors - is to have a vertical splitter available for all your coding windows.
Yes... we don't.
Please implement this, hack it in, make a plugin, ANYTHING. It's just silly that it's not available while a horizontal splitter IS.... !