There is no game that saves all the data as-played in the sense you seem to mean. Data isn't just streamed to disk or anything. Regardless of whether a button is pushed or a timer is tripped inside the game program, and regardless of whether or not the entire game state is saved or only art of it... a function moves some data to disk, that can later be read back. That's it.
I seem to have said something wrong.
I did not mean to imply that any game state is ever fully saved, or fully streamed. Only that the data to be saved (for whatever reason) is traditionally done in a single step (such as pushing 'Save Game') or in an 'as played' step where it occurs almost immediately after savable data is available.
In terms of starting a new game or loading a savegame, the difference there should be minimal. The amount of code for starting a new game or loading a savegame are both trivial compared to the amount of code for actually running the game, which is the same in either case. It's like walking in your front door or your back door; yes, both are different -- this is obvious, but you get into your same house either way. And those doors are just a very tiny part of the complexity of your whole house.
Again, I seem to have said something wrong as that is essentially what I was trying to say.
Just to reiterate for the sake of clarity…
When the game starts the relevant data is either retrieved (from a serialized location), or created (from new processes), based on whether or not it’s a saved game that’s starting, or a new game. Even if that data is nothing more than the player name and location, a saved game places them where they last exited the game and a new game places them where all new game players start… In the end, it is the same game that is running.
In more complex scenarios the developer must consider if any serializable data is relevant upon any player action.
Such that, entering a room will always check for the serializable variable that says if it’s been entered or not already. A new games flag is unset, where the saved games flag is. The question becomes when
that flag is to be serialized.
Did I explain that clearer?
Note: I sometimes tend to get a bit esoteric when talking about things I am new too and I apologize if I complicate these conversations as a result. I am sure that once I get more familiar with the normal programming parlance it wont be as much of a head ache to deal with my questions...