Lobster wrote:
I'm just wondering in terms of whether it's worth keeping those little
offcuts of tube from a job rather than just binning them, and/or whether
its worthwhile ever lugging out redundant tubing from previous
installations while the floorboards are up...!

It won't make your fortune, but if you save up the bits (including
valves, stopcocks, taps etc.) you can send them off for recycling
at your "tidy tip". Plumbers do keep the bits, as quantities mount
up and become worthwhile.