Subleasing Good or bad idea?

Lately I have had this idea of sub leasing properties but I do not know if it would be a good idea and what all would be required (insurance, legal docs, etc..), I am new to real estate and this would only be more  for a little bit of extra cash until I can get myself better established.  My other concern would be what kind of properties would work best if there is such a thing and how much risk is really involved if I were to pursue this any further? any input would be greatly appreciated.