Sleeping bag or travel liner?
Weight is a key question on the Camino. A sleeping liner seems to be a much better solution with its 200-300 g weight than a 600-700g sleeping bag. From the middle of June until middle of September, when the outside temperature is always above 30 C travel liner is adequate. Don't forget that there are no air-conditions in the albergues, so summer nights are too warm to sleep in a sleeping bag. In autum, winter and spring always take a sleeping bag with you but choose the lighter version (600-700 g) which is comfortable between 10 and 20 C. All the albergues has heating, so the temperature never goes below 10 C.
Nothing unnecessary just exactly what you need for your Camino