Having a stash of cash is critical for a peaceful life. Cash is like the grease for life. Grease helps a machine operate smoothly. Cash helps your life operate smoothly.
Need to make a move? Need to make a quick trip? Want to seize a new opportunity? Unexpected expense? Having a nice pile of cash will allow you to operate smoothly and more effectively, even if it's not the only thing that's important for effectiveness.
That's why I think you should have more than just the requisite 3 to 6 month emergency fund. You obviously shouldn't forgo real investment opportunities that will grow your wealth by hoarding cash, but you should make sure you keep some powder dry for those unexpected events, both good and bad.