One more point to what has been mentioned by Mathan and Vivek.
Regi.exe is required when you wish to use it for Repository based development (primariliy XS development). It is not mandatory to connect to HANA server. If you wish to connect to HANA from Studio and perform development related to HANA Information model (Attribute, Analytic, Calc Views) then regi.exe is not required.
Regards,
Ravi