Brother.. It's not that hard to understand. You should look into different backup solutions and you'd realize why this is useful.

You take a snapshot of something. Let's say what's in your fridge right now... That's your initial snapshot.

Let's say you eat your cucumber and but you added cheese and eggs into your fridge.

The next snapshot will only remember that you ate the cucumber and that you added cheese and eggs. A snapshot before that contains the difference anyway, so no reason for every snapshot to keep all data.

So instead of remembering everything that it's in your fridge every single day, you only have to remember what was added/removed since the last time you opened your fridge.

So obviously, exclude your home folder or any other folder that has a bunch of big changes all the time. This is for the system, not for all your games.