Because you don't want to change them again soon pain in the tail ..I only use professional iridium AC Delco and gap them at .60 do not use the ramp style gauge use feler gage and be very cautious because you can brake the wire ..on the plug .. just gap them the night or day before .. and take your time doing it ..
And if your changing the cap and rotor use AC Delco also and a good set of wires ..trust me .. you'll thank me later