Save File
'Save' stores the game at that very moment in the save you are currently playing. You will override/update the save you are using.
'save as' creates a new copy. When you save as and continue playing in the game session, you will be playing in your new save.
It works just like save and save as in other programs like 'word', excel,...
I wouldn't create a save as every single time because that creates a lot of save files which can cause longer loading times.
Just for the sake of being complete: If you start playing next time and you are on the main loading screen, you should know resume game (the button with the picture of your last played sim) will automatically take you to the last save file you saved. Load save will give you a complete list of all save games to choose from.
