What would happen if you installed a set of plugs out of the box without them being "properly gapped" like it says in the manual. Will it really make a big difference?

 

well all the plugs come at about the same gap out of the box so it's a matter of how far off it is from factory spec. if it's too small then you might have some rough idle, if it's too big you'll wear your plugs, cap, and rotor out quicker due to the increase of required voltage and if it's way too big you'll misfire. just pull em out and gap em

 

yes, the farther you are from the correct gap the less preformance you'll have. too small a gap will decrese the size of the spark exposed to the AF mixture and too large a gap will weaken the spark as it tries to jump the larger gap.