reducing the transmisibility of reduces the effective R value, which reduces the "herd immunity" threshold.. which stops the virus. (i.e. wear a mask)

but also...

the mortality rate has fallen because we know more now than we knew 6 mos ago. That will continue. If you slow it down you get that benefit + the benefit of having fewer people exposed before we have a vaccine.

"the sooner the better" is true if "better" is measured as "most deaths possible"