Field help (SPCPLISEA) 

The search groups are used for the association of logical price list sets, which are evaluated by priority within the same group.
After the search group evaluation, the price list coming from the price group that is the most favorable for the customer is taken into account, based on the calculated net price.

It is possible to define up to 10 search groups (0.9). if no group is determined (all the price lists have a value of zero), the priority apply to all the price lists.
SEEINFO Search groups do not apply to grouped price lists