Usually we keep LAC = RAC .
There are no risks in keeping that configuration, rather it is the best and prefered configuration.
One LAC may contain 2 to 6 RACs but that is not prefered since it may lead to unnecessary RAC updates and thereby increasing the signalling load.
The moving GPRS traffic is usually low . If however, the GPRS signalling load increases then one RAC can be splitted into two.