Yep, that's the standard answer. But (a) why does the average investor care about short term liquidity? Mutual funds only let you sell once a day and most people are perfectly happy with that. And (b) what good is liquidity that disappears when you need it most?
It's a self-serving argument at best. I sometimes wonder why the whole thing couldn't be replaced with a giant daily auction.
Mutual funds (along with pension funds and other large institutional investors) move tens of billions of dollars into and out of various positions regularly. Speeding and simplifying those transactions reduces opportunity and transaction costs and (theoretically) benefits all holders of the fund.
Keep in mind that we're talking about prices here. What is a stock price?
If I put in an order to sell one share of GOOG for $1, would you start to believe that the market price of GOOG was $1 per share?
A market price is only as valid as the degree of consensus. Increased liquidity means that there is a high degree of consensus about the current price. This means that one can feel additional confidence that one is getting a fair price.
The main concept to think about here is an order book. Think about the psychology behind orders that are a ways away from the best price (both bid and ask). Those parties are willing to transact, but at a premium. In other words, they prefer to hold unless a sweet enough offer is made.
Thus, for a very large order one has to pay that premium.
It's a self-serving argument at best. I sometimes wonder why the whole thing couldn't be replaced with a giant daily auction.