Sump Pump and Floor Drain

Just a basic question. Why would home need both a sump pump and a floor drain. If the sump pump takes excess water out, what purpose does the floor drain serve? Sorry I'm so naive!

A sump pump is for removal of clear groundwater from BELOW a home's floor and foundation. Most areas have ordinances which state that this groundwater should not be pumped into the municipal sewer system as it can overload sewage treatment plants with water that does not need to be treated.