The primary advantage of an adjustable handle is comfort. You'll get extensions with folding shovels. You can use these to adjust the height of the shovel for a certain purpose. You also don't need to bring a large shovel. If you know you're going trekking or camping in a place where you won't need a big shovel, you can leave all the extensions at home and bring other items instead, such as a tiny first aid kit, etc.