The following is from the INSTRUMENTATION section of the DellOpenManageEnvMon MIB:
Environment = DellOpenManageEnvMon: DeviceID
DeviceId will represent index of the entity. For example say fans are created using x.y.z oid which has 4 values for 4 different fan instances, then while instrumentation we need map the values based on index. i.e. x.y.z.1 for Fan1 , x.y.z.2 for Fan2 etc.
If you don't provide this then mapping may cause some problem, it may not know the index to map. While polling it may poll for x.y.z oid not x.y.z.* and will get reply more than 1 value, hence status value will not be updated.