If you have an idea for a game mechanic, you might not want to build an entire inventory system or a main menu from scratch just to test it. Downloading a complete project gives you an instant framework. You can swap the art assets, tweak the physics, and suddenly, a generic template becomes a prototype for your unique vision.
Many developers release their finished game code for portfolio purposes. unity complete projects free download
Complex multiplayer frameworks and custom rendering pipelines. If you have an idea for a game
Do you know of a specific free project that helped you? Let me know in the comments. tweak the physics