The problem with save systems really isn't finding a place where you can save your game state, it's putting your game data into a form that *can* be saved (i.e. serialization & deserialization). And even then, the problem is not so much the low-level serialization itself (most game engines have support for JSON, BSON or something similar) but determining what parts of your state need to be saved and what parts don't, reinflating the saved data into a functional game state, making sure that savegames from previous versions can still be loaded, and testing the whole thing, because forgetting to save something that needs saving can result in profoundly weird bugs that are extremely hard to track down.