One thing that I find to be unhelpful, typically, in these sleeping bag versus liner threads is that more often than not, when I read through one, the only people contributing are pro-liner ones, which can give a false impression of what the typical pilgrim's needs in these matters may actually be.
Whereas in nearly 30 years on these silly Caminos, I have come across exactly one pilgrim sleeping only in a liner, and as a matter of fact that night was a bit cooler, and he did not seem comfortable.
I do get that there are some pilgrims from northerly countries that are quite cold, and so may need less bedding than others. But this is quite outside the norm, and a genuinely cold night is always a possibility, especially next to the Atlantic or high up on the Meseta, and blankets supply in the Albergues is far from being guaranteed.
Now, these days I am mostly sleeping outside, so in rather different conditions.
But as to last night, a fairly strong wind between about 6 and 11 PM blew most of the day's heat away, and in the 3:30 to 6 AM pre-dawn, it was chilly enough that I needed to zip my sleeping bag up completely to keep warm until I woke up, for the first time this year. My big black woollen pilgrim's cape that I'm using as a blanket/"liner" wasn't enough to keep my arms warm in the early morning.
As to some saying you only need a liner, but pack some night clothes to keep warm, I just can't see why not pack a lightweight sleeping bag instead.
And I've seen too many contributions from those who only packed a liner from forum advice, and then on cold nights seriously regretted it.
