In addition the game data and save files are separate so you can delete the game data and install another game and when you want to go back to playing the original game you repeat this process and you don't have to start over because you have the save files.
Also you gotta consider the fact that installing a game will save you more time in the long run assuming that you will actually play the game and try to finish it. All those 10-15 secs load times add up.







