[grotorea]

Not financial expert but I think "liquidity in the market" would be more of a high-frequency trader thing. The advantage to everyone else is that good investors inject information into the market and move prices towards their "correct" price earlier, preventing other investors from buying overpriced securities. Of course they make a profit by capturing the chance to buy underpriced securities but there's still a benefit. It also ought to mean financial resources are better allocated towards companies that are profitable and/or will make a profit in the future.

tl;dr: (Actively managed) funds and investors are the Gosplan of capitalism.