i used 2 single all last year and it worked great. anything you didn't want or couldn't keep was released easily, and with minor harm done to the fish. also, i found it stuck better when you set the hooks. same reason fish rarely ever shake off a plug. it does effect the roll, but not very much, and you can adapt and get the same roll anyways. also, singles are much stronger, i use gamy's (5/0 for chovies and a combo of a 5/0 and a 7/0 for herring, cut or whole) and i've never had one break or bend. plus, they are easier to sharpen, and cost less.
sorry for ranting, i'm just a strong supporter of singles, mostly because i saw a lot of people releasing dead coho last year.
Thanks Captain Dudds