intersection of meshes in centrifugal pump
 

hi everybody
i want to import 2 meshes of a complete pump, impeller mesh(rotating part)and casing(stationary part) but when i import 2 meshes and i want to create the frozen rotor interface between them,meshes have an small overlap region i mean the two side of interface is not connect to each other in this case i think i should use the intersection option in interface window in cfx.now my question is :
what is the best model of intersection for my case?
what happen if i dont use intersection?
thank you