MME can associate "paging priority" with a S1-AP paging message for an UE.
When eNodeB receives S1-AP paging messages for a set of UEs, It can prioritize some UEs out of total UEs present. There is limitation of paging records (i.e 16) can be send in one RRC paging message.
So if eNodeB has more than 16 UEs to send page message, it can prioritize them.
Usually MME includes "paging priority" when some high priority data is coming or some bearer creation is on going etc. It is up to operator policy when it want to include "paging priority". It may be based on operation or subscription as well.