what happens when im using a regular script, and what are the advantages of using a local script
Using a LocalScript will make CLIENT side changes. So if you're making a GUI that displays the amount of money the Player has, a LocalScript would be easier to use to access the Player and his data.
Use Scripts because the Gui always goes to PlayerGui so you don't have to worry about that and also Scripts are easier. I used Scripts for my Guis and it worked just how I wanted it to, no players could see what I pressed and what Guis became visible from pressing on TextButtons. So the answer is Scripts.