what exactly is the purpose of changing your gear ratio in the winter? i know of people who normally go for a lower gear ratio when winter comes around but no one has ever explained to me why.

right now i'm riding 48x16 but i have a 14t cog sitting right here that i'm eventually going to put on. would it be wiser to keep it at 48x16 for the winter, or even go to 48x18?