Virtually all my plumbing will be threaded through studwork, so plastic pipe is by far the easiest.
But some runs have to be copper, e.g. boiler to thermal store, vent pipe from store etc.
Other bits would be better in copper for the rigidity/robustness e.g. exposed pipes up to appliance taps, network of stuff supporting pumps etc.
So that would mean overall, almost every pipe run (hot, cold, heating) will be a mixture of plastic and copper.
I can't see any disadvantages to this, I've used plastic a lot with never a leak I can recall, nor any leaks in solder-ring fittings in new copper pipe (and very rarely a leak in reworking existing copper pipe - though compression fittings have occasionally had hard-to-cure drips).
So I can't see a downside to mixing plastic and copper as appropriate
- anyone think differently?
(Obviously such earth bonding as necessary will be done around boiler etc - and there's no need I can see for electrical continuity on any of the pipe runs)