Is SF4 Polar or Nonpolar?

Answer: SF4 is polar due to the presence of a lone pair of electrons leading to electron-electron repulsion and thereby a region of partial negative charge. However due to the other atoms in the structure being the very electronegative fluorine the partial charge on the sulfur will be quite de minimis.   

Sulfur tetrafluoride due to the effect mentioned above has a relatively low melting point of -121°C and boiling point of -38°C. This means that the compound is a gas at standard temperature and pressure. Due to the large amount of fluorine atoms it will react quite violently with water or water vapor. This makes the gas quite corrosive and toxic for humans, generating hydrogen fluoride and sulfur dioxide within the lungs. It is recommended that humans never be exposed to this molecule.  

SF4 Ball and Stick Model. Created with MolView.

How is SF4 utilized in the real world?

The most common usage of sulfur tetrafluoride is in creating compounds that require the addition of fluorine atoms. Specifically the combination between alcohols and SF4 typically produces many different kinds of fluorocarbon compounds. These in turn have their own specific pharmacological and industrial applications. This is similar to the kinds of applications for other compounds with a large number of fluorine atoms including NF3 and SF6.