"Basically my question is: prevention or just treatment?"
Both! Put it on your feet (I really focus on and between my toes) first thing before breakfast, or even the night before. No reason you can't also touch up spots during the day. You can also apply it on top of duct tape, or along the edges of leukotape to prevent any adhesive catching onto your socks. One way to experiment is to apply it on one foot, but not the other. I tend to only use it when I anticipate a lot of cold and wet, or when I know I will be pushing myself beyond my normal limits. Otherwise, I would rather just find a foot system that works for me without the expensive goop.