what kind of saw to cut plastic
A hacksaw (coarse blade) could be used on plastic, but not wood. A carpenters' saw would be used on wood. Power saws are always the most efficient, but of course it depends on what type of cuts you are doing.
First and foremost, the benefit of using these hand saws is that the presence of the thin blades allows them to cut soft metal, plastic or wood with a very small kerf, maintaining a neat and clean edge on both sides of the cut.