If you have an internal hub gear like the 7 speed Nexus, it's not even an issue. Downshifting on a hub geared bike is easy and won't damage the cassette since there isn't one.

When I commute with my 3 speed, I don't shift down at the light since 2nd gear (direct drive) is set low enough that I can make most rolling hills without having to shift to 1st. I only shift to 1st gear if the grade is VERY high.