IMHO and based on some experience, camping should be considered as a just-in-case issue. There are so many lodging options along at least the
Camino Frances that HAVING to camp out is virtually a last resort. That said, I respect the preference of some to occasionally sleep under the stars. I just outgrew it, preferring a mattress if possible.
I see it (sleeping outdoors) in cases where there is literally no room at the inn and you get "stuck" between villages (very unlikely). Or the weather compels you to seek immediate expedient shelter. It CAN happen, albeit not very often.
I no longer bring a sleeping bag due to weight issues. However, this year I am using a double, nested liner setup I developed. It is a Cool Max Liner fastened inside a silk outer liner. Both are rectangular and weigh an all-in, combined, 540 grams in the stuff sack.
My fastening system to keep the two somewhat difficult liners nested, is four ping-pong balls, one in each corner secured on the outside by nylon, bungee-like, hair scrungie bands. As both liners had "pillow pouches," this corner fastening worked rather well. I used orange scrungie bands so they would not be easily lost. The four ping-pong balls and four baby bungee rings added 10 grams in total.
I also have an SOL (Survive Outside Longer) brand "Escape" bivvy sack that weighs 238 grams. It has a reflective interior and a 1/4 zip. I expect that will remain at the bottom of my rucksack for the entire Camino. But it is my just-in-case "emergency" item.
These three components provide me with a flexible and scalable sleeping system allowing me to go from a heated albergue all the way down to sleeping under the stars if need be - at least in May. Taken together, the components (nested liners, and bivvy sack) weigh about the same as last years' Snugpak "Traveller" sleeping bag. However, I think it provides more flexibility.