Please, please, please - context is important. If you are relaying your experience that you didn't need to use a sleeping bag, you really do need to say what time of year you were walking, where you started, and did you rely on finding albergues that provided blankets.
I started in SJPP in Mar 2010, carried a +5 deg C bag and light liner in a compression sac, and would not walk at that time of year without a bag. It allowed me to stay in
- the old school gym in Zubiri where there were mattresses but no blankets, and
- at places like Granon and Espinosa del Camino - brisk is a barely adequate description for both places. Both provided blankets but it was more convenient wrapping up in a sleeping bag rather than trying to stay under a pile of blankets.
Without a sleeping bag, I would have had to think about more expensive accommodation options or walking on to the next town to find a warmer place to stay.
My own view is that a liner is essential for any trip where you will be sharing your bed with the many dozens of people who have previously slept in it. I don't treat it as an option in those circumstances.
Regards,