Why would you use a " - " DVD burner?

I don't know where you got that idea from, but its not true. The general idea is -R is more compatible. This seems true with testing that some unbias sites(DVDplusRW.org doesn't count). The ratio is like -R is compatible with about 97% of the players out there and +R is with about 88%. There are minor differences between the two formats, but its really insignificant. +R basically came out because Philips didn't want to pay royalty fees to the DVDR Forum. So it really doesn't matter what you get now, both will be compatible with most newer players.