Mainly what it does is make the market more volatile, and it is a big factor in how you have to trade. The market can move in the opposite directions it otherwise would, simply because of the options put/call ratios and expirations.

And counter intuitive to the above point, it stop thr market from rocketing or plunging. Because people pile into options in the direction the market is moving, and the more option pile on, the bigger and harder the reversal ends up being.

So it helps to analyze how many options are at what strike and expiry, to know when to make trades.