We had about a 10" gap behind our machines because of the way the dryer vent was installed. That gap was pretty ugly and stuff was always falling back there. PLUS, the outlets and water hookups just added to the list of things I hated looking at in there.
I had to figure out a way to improve this. If I had a wall on both or even 1 side of the machines, I could have just installed a removable top over my machines.
BUT, I decided to build a table since I wanted a removable option that could also hide the left sides of my machines.