Yup I agree with sheldon, but its a trade-off if you are working with sites that are seperated by large distance e.g in small cities in rural ares, and there is no possibility of Handover also if you Abis cost is high then it is sometimes preferred to use different LACs for non-handovering clusters of cells. This helps in reducing the paging load on the RSL, and there is no issue with the excessive location update as the LAC boundaries are non overlapping..
Also as far as the difficulties are concerned in some vendors having same Cell-ID with different LACs can cause stats pegging issue so Cell-IDs need to be unique. as in those vendors Cell-ID is used as a unique identifier, so not a very good idea.
I am not sure weather Alcatel has Cell_ID only or Cell_ID_LAC combination for identifier for pegging stats as I have experianced this issue in Alcatel previous release.