The reason that pellet grills/smokers have become so popular is that they are a way to cook with hardwood and get that nice smoke flavor into foods with very little effort and time to monitor them.

As long as there are pellets in the hopper you don't have to manage a pellet grill the same way you do a charcoal or offset smoker (fire management). With a pellet grill/smoker its simply a case of setting the temperature on the controller and letting the pellet grill get on with it. 

In some cases, with pellet grills/smokers that have WiFi connectivity, you can monitor the temperature of the pellet grill, adjust its temperature, and monitor the internal temperature of the meat through an App on your phone from anywhere. You can go to the game, down to the shops etc.

Some people even leave food smoking away on their pellet grill while they're asleep or at work. The point being, a pellet grill/smoker requires very little of your time to monitor it, and for most people, time is at a high premium.