When it comes to something like meat, the biggest thing is that the salt can penetrate into the meat itself, rather than just sit on the surface. Same goes for things like potatoes or pasta.

Other than that, I couldn’t really tell you, on a technical level, but you can be sure it boils down to “chemical reactions.”

If you’re curious or skeptical, you can experiment pretty easily. Make a batch of tomato sauce, and seprate it into two portions. Salt one before simmering it for a few hours, and the other one after. Most people will be able to taste the difference.