It builds a habit and moves you closer to your overall goal. It's similar to a common suggestion for writers who want to write a book: open an editor and write at least one sentence per day. Or doing at least one push-up every day.

No more zero days, so to speak.

Starting is often the hardest part. An easy task makes it harder for you to talk yourself out of it. It also keeps the ball rolling.

I think the OP meant "code" in its purest sense - writing something for themselves, not necessarily pushing the contributions to GitHub as a part of gamification.

You don't have to do it if you're disciplined. I struggle with it and I find tiny daily habits useful.