It's a must-have for me. For the most part, it serves as the outside bar, so there's less traffic through the kitchen. But it's also really nice being able to cook without steaming up the trailer. It's also nice keeping the inside quiet when there's late-risers sleeping in.
My outside kitchen has a proper 3-way fridge, which I would also consider a must-have. The small apartment fridges that come in most trailers are not energy efficient at all, so maintaining power to those can be a PITA unless you only do short drives, and run a genny at camp.
My trailer has ample ground clearance, so it puts the kitchen at the right height for usability, and you can stand under the door without bumping your head.