It's just a camera view - it doesn't have to change the game. There are several games that give you the option of switching from 3rd to 1st Person (Skyrim did it pretty well).
I just prefer to see the world the eyes of the character, and not like a little bird following from behind. It gives me the feeling that I'm observing the main character instead of actually being him. Just personal preference - but I appreciate when developers give you the option.
I also liked having the choice to play in either perspective in Skyrim, but let's not try and understate the importance camera view has on the style of combat offered by games. It might not affect the overall story, but player perspective is inherently tied with not just combat mechanics but things like movement and object interaction.