I've had one for years, just means no matter which weird angle you sit at the mouse always has mat, also I find the small amount of extra padding on my arms and wrists nice
I guess. I've got a kb wrist rest and wired stuff so it's possibly less useful for my setup. Although, when I wear the mouse bit out it would mean I could rotate it for double life.
Not sure I see the point in that much coverage. I don't move my mouse over my KB for example.