Are you talking about Mike Holmes? (Holmes on Holmes?)
Screws aren't required for framing as far as I know (I think it is his personal preference but not just to advertise the Dewalt Impact Drills)
Well the only time I have used plastic boxes is in residential work - 52 suites (loomex). Haven't heard their reasoning about using only metal boxes only.
To Quote the code book
12-3000
(2)Non-metallic outlet boxes shall not be used in wiring methods using metal raceways or armoured or metal-sheathed cable, except where the boxes are provided with bonding connections between all conductor entry openings.
