1. Totally agree with Madrab. Like any other system, provided its installed and tested properly and in accordance with the manufacturer's instructions, plastic piping / fittings will do the job as well as copper.
2. However, copper:
2.1 Requires fewer clips.
2.2 Is more resistant to rodent attack.
2.3 Can be recycled indefinitely.
2.4 Looks better if on show, albeit this is a personal opinion.
Agree with all but 2.1.
I have deliberately installed plastic pipes in places where it's impossible to use clips (narrow gaps, boxing in going from floor to floor, etc.)
Plastic pipes are flexible and providing they're properly clipped near the joint, they can happily be unclipped in those situations.
Unlike copper which needs to be kept in place with clips in the exact spots.
I have come across full lengths of unsupported copper pipes that had sagged to a banana shape and eventually leaked at the joint.
This won't happen with plastic because the joint, at least with hep2o, can be twisted after being fitted, it's designed to do that.
Said this, if copper is fixed in place properly, can be a lot more durable (seen in my own house original pipes).
But we don't know that for sure because plastic pipes have not been around long enough to say.
Time will tell if the 50 year guarantee given by some plastic manufacturers was done because the product is durable or just as a marketing strategy.