It really depends on if it's a wind-heavy storm or a rain-heavy storm and where you live. Here in Greenville, a rain-heavy storm means lots of flooding which is Bad, and a wind-heavy storm means a few pine trees get toppled which is slightly less bad. A Cat 5 means "Get the Hell Out" no matter what. A 4 means "Pack Your Bags and Get the Hell Out". A 3 is on the border--could be bad, could be a big storm. 2s and 1s are just big thunderstorms with swirly wind. This is all my experience, though. The National Weather Service probably has more scientific explanations.