Depends on the weapon/situation, but in general..no. Such weapons as the Springfield Armory XD have both a trigger and grip safety (passive), hence making an additional safety somewhat mute. Weapons with a de-cocker provide somewhat of a "saftey measure" if kept with a round in the chamber. So, would an additional safety be necessary in this case? It depends.
If I kept a round loaded within the chamber at all times, I might see the need for the additional safety, regardless of the weapon. This is due to the fact that, God forbid, someone was able to take my weapon from me, they would have to figure out how to take the weapon "off safe." This could buy one a few "life saving" seconds. But, I do not keep my weapons this way, so I dont feel the need for the extra hardware as of yet. Now, if I were LE then I probably would have no problem with an "additional" safety.