[vharuck]

It's not only to keep the number of people needing hospital care below capacity, it will also lower the final proportion of a population infected before herd immunity has an effect [1]. By slowing the spread, it becomes more and more likely somebody exposed to the virus has already recovered and is immune.

[1] https://www.r-bloggers.com/flatten-the-covid-19-curve/

[DougN7]

To be more likely that the next person to get it is already immune requires millions and millions to be exposed. That’s exactly what herd immunity is. So how long will it take millions and millions to get this immunity.

[vharuck]

Sorry for the ambiguous wording: more likely than before a period of strict isolation to be immune. There would still be a spike after isolation is lifted, but the total number of people infected by the end of this wave will be reduced.

Of course, the question is "how much" and whether that's worth the cost. But not overloading the ICUs is valuable on its own.