Value mapping maps one value to another and the function works perfectly for floats. Positional mapping distributes the input as evenly as possible to the output and the function as is doesn't do that ...

In Arduino applications often the 'raw' value of a sensor is mapped upon a more usable value. E.g. the value of analogRead() 0 .. 1023 is mapped onto 0 .. 5.0 Volt. This is often done by the map() ...