Backend Characteristic Values

Hi, Just curious if anyone has any hard and fast rules as to whether the characteristic values should be numbers or something descriptive? I always thought it was best to go with numeric codes instead a descriptive text code.? I always thought code was better because the system didn't have to figure out what the next SID to be assigned was and that the SID just took on the value of the characteristic when it was a numeric code.

Opinions are appreciated!

Material   Description
0021       Nexgen Hi Capacity IPOD Flash Ram
or
IPODRAM    Nexgen Hi Capacity IPOD Flash Ram