It’s crucial that as the game production progresses, you must have a working product. At the end of your coding session, you project must work (at least to some extent without crashing). By always having a working version you know that the in the next session you can continue working on the game, instead of trying to find out what’s wrong. It’s also practical to have a working demo in case you need to show the demo to someone: you’ll always have something to show.
Remember: Have a working version of your game before you stop coding for the session.