The short answer is a long strap will last longer.  Depending upon the application, the strap thickness itself for various sparkplugs will also vary.  A detriment to side gapping or ground strap shortening is that the strap will wear at its tip.  This can ultimately cause enough wear at the the end of the strap in a high mileage situation that a specific gap cannot be maintained assuming there are enough miles put on the plugs in which to see this.  In a performance application, it’s unlikely to ever see this number of miles so any potential gain in performance and/or efficiency more than offsets this happening.  Where the strap is covering the center tip, the ground strap material is being eroded directly above the center tip and can potentially be regapped with a wire gauge to get the gap back into spec.  Lots of miles are being discussed here though but with the newer cars going 100K+ miles on a set of plugs, it’s a valid consideration.  From a spark plug manufacturers standpoint, if it aint broke, why fix it point of view but realistically, it’s much easier to keep the strap longer for both attachment and manufacturing variability reasons.  And spark plugs are like anything else on an engine not specifically made by the engine manufacturer in that the OEM versions of the plugs are normally made to the engine manufacturers specifications.