The salt can help “seed” the boiling, by providing nucleation sites for the bubbles to form. So, you end up with more bubbles, but they are smaller. Of course, this effect is only applicable before the salt finishes dissolving, so you’re only going to notice it if you throw salt in when the water is already boiling or close to it. Chemists will use boiling-chips (little rocks that don’t dissolve) for a similar reason to ensure a smoother boil (smaller bubbles means less splatter, assuming you put them in at the beginning… you definitely don’t want to add boiling chips after things are already hot or you’re gonna end up with even more splatter than doing nothing).

There are certainly energetic effects caused by the dissolution of salt crystals, but unless you’re starting with deionized water or using a crazy amount of salt, the effect is gonna be pretty negligible.