Why shoot +P in 3" barrels , light frame pistols ?

Most standard loads will not expand properly, which can cause
over penetration and a small wound channel, like a FMJ.

There are about three 115gr bullets that will pass penetration test........
Several 124gr will pass the test and at least three quality 147gr bullets will pass the test.......

and these loads with modern bullets and powder were designed
with just enough fps to do the job and keep pressures as low as possible on todays pistols
than can shoot these loads.