How is Florida Power and Light a monopoly?

Question

with that how does it serve as an advantage and disadvantage over competitors?

Answer 1

If FPL had a competitor, the rates in Florida would probably be lower.   For example, cable, phone and Internet service, Comcast is now competing with Verizon (although Verizon is not in all areas yet) and the rates have gone down.  (since the triple play deal has been launched)

Answer 2

It is very simple:  Do you have any other choice than FPL to get your electric power from?  If the answer is no, then it is a monopoly.

Utilities are legal monopolies in that the state regulates their rates and does not allow other companies to compete with them.