What are the advantages of a non-submersible pump?

Non-submersible pumps can be petrol driven, do not have to waterproofed and therefore will generally be more powerful, and can pump more water and do it more economically. 

If a problem occurs the pumps are not underwater and can be accessed more easily. 

Because they are not a tight and sealed unit they are easier to maintain.

Some are self-primed.