I will give a long round-about explanation/introduction/lecture before answering your question! It's impossible to answer a question about a detailed feature on a single item of clothing. As others have said, it is the clothing layering
system that matters.
To plan your layers, start by picking a combination of clothes that you would wear for a long walk on a "typical" day at home, assuming a sunny day with the temperature starting at 5C and going up to 25C. For me, that is typically:
- light base layer t-shirt or sleeveless tank top,
- light long-sleeved t-shirt,
- button-up shirt with long sleeves to protect from sun and give a small amount of insulation/windbreak,
- merino wool buff and lightweight gloves
That is for typical walking when it is not raining. As the day warms up, you take off layers. First, the buff and gloves come off (without needing to stop and remove backpack). Then after a couple of hours I might stop and remove layer #2, but then put #3 back on.
If the weather stays chilly or is windy or rainy, I wear my lightweight rain jacket and, if necessary, my rain pants, over the same walking layers as listed above. Those items are almost always enough to keep me warm while I am walking in March, October and November, through weather ranging from 0C to 30C, from blazing sun to pelting rain. I have rarely worn a "fleece" while walking, whether 1/4 zip or full zip.
You should have something warm and cosy (be sure to keep it dry) to wear in the evenings when your body is tired and easily chilled. That is when I use my full-zip fleece, often with a sleeveless down vest. Either of these items can be used during the day in case of "emergency" (really unexpected cold weather) or worn to bed as an extra layer if the albergue is unheated.
As to your original question about the zipper for a "fleece," it depends on what you are using the fleece for. My medium fleece has a full zip as it provides the most flexibility for temperature control.
Having said all this, I realize that many people take different things, such as an all-purpose "fleece jacket" and are very happy with their choices.
