Using an Index Fund as your Savings Account... a new strategy?

[Tiffany Onwudinanti]

I was watching a Meet Kevin video (here is the link) and he talks about the detriment of ordinary savings. He then mentions how putting your savings in an index fund is a better bet, and not just keeping your money dead in an account. Would like to know y'alls thoughts, especially those who do this savings strategy. 

I use Vanguard for my Roth. Drop any index funds gems if you know any.