hey andy seeing as my explanation lacked lucidity i found this for you it beautifully explains it:
Price discrepancies, although at odds with mainstream finance, are persistent phenomena in financial markets. These apparent mispricings lead to the presence of “arbitrageurs,” who aim to exploit the resulting profit opportunities, but whose role remains controversial. This article investigates the impact of the presence of arbitrageurs in Indian financial markets. An arbitrageur, indulging in costless, riskless arbitrage is shown to alleviate the effects of position limits and improve the transfer of risk amongst investors. When the arbitrageur behaves non-competitively, in that he takes into account the price impact of his trades, he optimally limits the size of his positions due to his decreasing marginal profits.