It all depends on what kind of gun and which caliber you are shooting them out of. For most 9mm loads and Magnum revolver loads you should be fine with SR primers. For light PPC loads and such, you might have to adjust your load.
The difference is how they light the powders. Some rifle powders won't light good with SP primers but will be ok with SR or SPMag primers. You might gain about 25fps.
Safe is relative. If you are loading at MAX loads, I would reduce it some.