A lot of games start with their intros and vendor videos, and then show a "Press Start" screen before the actual main menu.
I never quite figures out the purpose of this. Why not go to the main menu directly? The only possible explanation that made sense to me is that when multiple controllers are connected it allows to identify the one that the player wants to use.
The historical reason for this is somewhat different from the current reasoning - previously it was to have a 'safe' screen to go back to which was always resident in memory, so that if the game had gone to a demo loop and the player touched the controller, it could instantly return to the start screen and let interaction commence with no delay.
However typically these days it serves another purpose. For recent generation consoles, the start screen is deliberately user-agnostic. Nothing on the start screen requires knowledge of which user is actively playing the game. You get to the start screen without loading any save data, and without requiring a user to be logged in. So you can get to the start screen quickly and without having to show any TCR compliant messages.
Requiring the user to press start gets you a key piece of information: which controller is the primary controller. It's not necessarily the first or only controller connected, and you might have several equally valid controllers to choose from. You don't know which one the user has actually picked up though until they've pressed a button on it. Once that controller is used, it will remain the primary controller for the rest of the gameplay session.
On XBox 360 (and most likely other consoles), finding out what the primary controller is also typically gets you another bit of information: which user is playing the game. Because each user is bound to a single controller, you know which user is playing, and from that you know which save data to load. Many / most of the content is bound to specific users, so it's important to determine who is playing the game before continuing. If no-one is logged into the console, games will typically prompt at this point for a user to log in, or ask if the player is happy to play as a 'guest', i.e. without saving (because with no user, there's nowhere to save to).
You'll also find that, typically, changing users (by signing out and back in) will cause you to return to the start screen. This is because the relevant user-specific data is loaded after this point in the game, and the start screen is the easiest point in the user interface flow where you know exactly what data is loaded (none).
This is required by the console manufacturer as part of the standard Technical Requirements Checklist (TRC). One reason is to allow the startup screen to loop back to a demo mode if no one has touched the controller, this stops screen burn and makes it easy for a store to simply pop in a game and let it run looping action with no intervention.
Your guess is the secondary purpose, and that's the way it's used =)
As well as the reasons given above, arcade games are also another reason. Usually an arcade game will loop the menu/intro until a coin is inserted to start a game, however when ported to home consoles, the coins are no longer needed so it looks for a button input instead.
I recently added a start screen to my mobile game. The decision came after testing it on an older phone. The game front loads a majority of the assets into memory when the game starts, and was causing a significant delay between launching the app and getting the first feedback loop.
I realize there are many ways to solve this, but I decided to slap a start screen that starts loading the next scene in the background. When the user actually clicks the start button they get their first feedback of a sound and a fade transition. It also seems to reduce the load time, but this could be due to not having to stare at a black screen or stagnant loading screen after launching.
On old arcade systems, pressing the start button, initializes the seed of the random number generator. This seed is used so that every play session is unique. On newer systems, I don't have a clue, I guess it's just a habit.
Also see:
