Well, it depends on what you're cooking and how you're cooking it.

For instance, if you have food cooking on an upper rack away from the direct heat of the grates, the end result may be fine without flipping it over.

However, if you are cooking burgers/steaks on the main grate, you are still going to want to flip them over to cook evenly/consistently as you would on any grill/smoker.

While pellet grills can maintain a consistent temperature there will still likely be hot spots on the grates. Therefore, you still need to monitor and adjust the positioning of your food on a pellet grill as it cooks.