in addition to #6 above - excessive wear on the inside part of the soles can also indicate a need for additional arch support
often - but not always - excessive wear on outside part of the soles can indicate under-pronation / supination that can be the result of high arch with not enough support ... this can lead to plantar fasciitis
and excessive wear on the inside part of the sole can be the result of (excessive) pronation - which can lead to plantar fasciitis
in both cases the tendons / plantar fascia can lack the proper support and be subjected to excessive stress
because the tendons / plantar fascia do not have the amount of blood flow of a muscle and therefore recovery can be longer (and frustrating)