To the untrained eye, Facebook’s mobile web strategy looks like schizophrenia. In reality, it is a tiered system:

Type https://m.facebook.com into a browser today, and you are greeted by a paradox: a modern interface that feels like a time capsule.

(($%@Mobile~Site!!))What does the 'm' in m.Facebook mean ... - LeetCode

It often utilizes smaller images and simplified scripts to conserve bandwidth for those on limited data plans.

Best for: Getting comments and interaction.