What's the point of sandwiching the 7 days between tests? Wouldn't 7 days isolation, then test be just as good? The only scenario (ignoring actual technical fal

What's the point of sandwiching the 7 days between tests? Wouldn't 7 days isolation, then test be just as good? The only scenario (ignoring actual technical false negatives) where you'd get positive on the first, negative on the second would be a very late stage where infectivity was mostly over already at the time of the first test.