The Illinois State Police put a lot of +P and +P+ ammo through their aluminum alloy receiver S&W pistols starting with the Model 39 Model 439's. It is safe to fire +P ammo in a Model 39-2, but higher pressure ammo will accelerate wear. I would recommend changing the recoil spring in the 4 inch barreled S&W pistols every 3500-4000 rounds, 2500-3000 rounds with +P ammo.
Do you really need +P ammo? 20 or more years ago, yes. With modern rounds like Federal HST, Speer Gold Dot, and Winchester Ranger T, the only things +P deliver is more recoil, more wear, slower follow up shots and you trade adequate penetration for even faster bullet expansion.