pressure not power thats what it means. a catridge without a +p marking is loaded to a standard pressure regulated by saami.as time goes on improvements in firearms are made the pressures they can handle can be increased,thus the +p rating.this is seen in older caliburs such as the 38spl. the 9mm and the 45acp. the fnp in 9 and 45 can handle the +p, there is not a new pressure for the 40cal. now in most cases the added pressure makes more power but not always,what it does make is more felt recoil and more stress on the firearm. use it or do not use it, that is the real question.