Absolutely no reason to let cash stay idle. There are tons of opportunities everyday. This is especially so since Oct 2018 where day range has been very very healthy. It is up to us to grab those opportunities with our cash.
Staying in cash in the medium and long term isn't usually a great allocation of capital. Obviously it depends heavily on the environment and what investment opportunities you have available to you, but as you mentioned having stayed in cash over the past 10 years, you would have missed out on one of the greatest run up in asset values in US history (equities and real estate) and you were able to do it while using free leverage. But now that that cycle is coming to a close, you'd have to look to other places to put your money. I would advise you to be careful in staying in cash, as you could get double burned if inflation kicks up and then not only did you miss the asset appreciation during the zero interest rate period, but you will also lose value of your savings because of inflation. The fed can be your best friend or your worst enemy...
That is absolutely right. There are only rarely opportunities like we have seen in this last volatile period--which is not ending just because we had a big up day today.