The filters on most cars now are full flow filters that are there to catch any big chunks that might be in the oil (break-in particles, etc.) They are rated in the 10's of microns, but the add-on bypass filters are usually rated at under 10 microns, removing the smaller particles (although I have no idea what the rating on the P-115 or P-117 filters used in the AD era filters is) from a small percentage of the oil each pass. Eventually nearly all of the oil would pass through the bypass filter, removing the smaller particles.
I think that's a good thing, as wear particles (bits of cast iron from the cylinder walls, etc.) can imbed in the bearings causing additional wear. I think in the long run, it would extend the engine life somewhat, although most people now get rid of their cars before they have 100k miles on them, so it doesn't matter to them.
But my nicely restored S-2 cannister with the blue body and orange top just looks cool.
