Unless you have flood insurance, if water comes in from the outside, you're SOL. I have some steps that go below grade to a basement door. I'm still figuring out exactly what's changed, but water started accumulating outside the door and migrating into my basement to a degree where it was about to cause real trouble.
For small areas this stuff is the bomb. They weigh next to nothing and come in a bag. You set them down and as soon as water touches them, they swell up and block the tide. They're not perfect but they're super easy to use, very convenient, and affordable.
If you have a low lying door or window where you might need some sudden short term surface level water protection, this product is worth a look. I got mine at Home Depot for less than the cost they list on their website.
