Consider the following scenario:

 

A nasty storm strikes your neighborhood and knocks out the electricity. Trees and other debris are everywhere, power lines are down, and officials say it will be another day or two before power is restored. No problem; you wheel out your portable generator and pull the cord to start it.

 

Nothing happens...

 

The nearest small engine repair shop is a few miles away and you're going to have to do without any electricity until services are restored. Once things get back to normal, you take your generator to your local small engine mechanic and she says the reason why it wouldn't start is water contamination. 

Bre over at Chickanic on YouTube says, most (around 70%) of the small engine repairs that she performs are due to water getting in the fuel. All that can be prevented by installing a fuel shutoff switch, which only costs a few dollars. This can save a lot of dollars in repairs and help ensure your small engines will work when you need them to. If you want to watch the video, here she is.