Much depends on what stops the hammer/striker/pin. Most have an inertial pin, where the hammer or striker spring does not drive the pin into the primer, it stops a bit short, and the inertia carries it to the primer. 1911s don't really have anything to stop the pin but the spring, the pin extends out from the breech before springing back into the channel relatively gently to rest against the hammer face. GLOCKs, M&Ps, and most modern designs allow it to hit the back of the breech face at the end of the channel before rebounding, can be fine for thousands of dry firings as designed, or the face can crack if there is a defect. A few hit a pin, stop or screw, especially older pistols, and with questionable metalurgy, they can break a pin. On modern pistols in good repair, unloading, disassembling, function checking, and a little dryfire practice won't hurt it, and if it does, it's probably a defect the manufacturer will take care of, and something you should be glad you caught in practice. If you compete, or plan on spending several minutes doing dryfire drills, in excess of "normal" dryfire use, then snap caps may afford some peace of mind, weither that make a difference or not is debateable. Older stuff, especially firearms like CZ52s that are known to have brittle pins obviously should never be dry fired