I have a single invention that has many different applications. Do i need to file a separate non provisional patent for each different use?
Have you filed a provisional application?? if not i suggest to file a provisional application to block the priority date.
If a provisional application has been filed already taking priority from that file a non provisional application and express request for examination. If patent examiner feels that the claims cover more than one application then the examiner would request you to elect the one specific group from multiple inventions, for remaining groups you can file continuation or divisional applications.
Good question. In brief I would say: Need? No. Should? Probably yes. This leads naturally to the question "how many?", which has no simple answer, as it depends on your plans and the perceived value you hope to obtain from each additional patent.
Some reasons for filing one application (and possibly filing divisional applications or continuations as needed):
Control of costs - only prosecuting one patent application at a time is easier on the cash flow, even if at the end you will file divisional applications and cost could be the same.
Control of process - if you have several uses for an invention, it may take time to figure out what is the best use and what features of invention best serve that.
Control of prosecution - makes it easier to control the scope you actually obtain in each eventually granted patent and reduces cross-talk between the prosecutions.
Some reasons for filing multiple patent applications in parallel:
It allows you to focus each patent application on a different use of the invention. Often there are subsidiary inventions that are different for each application and may need separate description. You should prepare this separate description in any case, but filing separate applications tends to help the inventor's focus.
Licensing is easier if you have separate patents for each field of use.
Avoids the risk that the eventual patent will be considered to limited to whatever particular use you focus on in your "one" patent application.
Faster issuance of a licensable portfolio.
Just to be clear - legally, you can put as many inventions and/or uses as you want in one patent. What counts in the end is the claims. If you have claims to more than one invention, you will usually be required to choose which one to prosecute first, but you will usually be able to file a divisional patent application to the other inventions at a later time (country dependent).
Note: if you decide to go via the multiple-parallel route, you have some work to do on deciding which will be the patent with widest scope.