What is the reason to have LOC/VNAV landing method?
A VNAV with localiser approach is normally a backup to a regular ILS should there be a glide slope unserviceability. The use of VNAV  to manage the vertical portion of the approach would allow the use of APV minima which are normally lower than using a vertical speed mode. 

VNAV is a better mode when conducting non-precision approaches as the aircraft is still following a defined glideslope - albeit derived from a database - which is more accurate than trying to follow a tabled set of heights and distances using vertical speed.