In bmx, everyone started to go with micro gearing. 25-9 even 24-8. The problem is the chain only goes over 3 teeth as opposed to a 11t driver which would go over 4, 16t which would go over 6 or so. When you reduce the amount of surface area on the chain more stress is put on each link, theoretically increasing the amount of stress put on the chain. Kids were snapping chains right and left with 24-8, not to mention the sprockets and drivers wear rediculously fast.

*this is an extreme example*