The idea with either requiring very wide band or frequency hopping on the 900Mhz band is to make it so that usages of the 900Mhz band 1. are tolerant to some loss (ie: by temporary collision) and 2. don't collide continuously (by using wide band or frequency hopping).

It's a mechanism to try to make the 900Mhz band more useful to uncoordinated users.