Con: what about critters and seasonal flowers and such that you might have missed.
Pro: it seems my attempt to reduce brambles with cardboard and mulch only gave it more time to work on its root system. When they emerged a season later the brambles were pleasantly surprised to find all the wonderful wood chips.
I would use cardboard and mulch where you can. Perhaps use plastic where you know you need a hard core fix, like a solid poison patch. Don't feel you need to clean it all up, open, fertile land will sprout quickly with problem plants you may not currently have.