I have an extensive cd collection which I copied to hardrive many moons ago. Probably in excess of around 800 cd's. How does an online streaming app assist me in that regard?
It assists you tremendously. Both Play Music and Apple Music allow uploads - 50k songs for the former and 100k for the latter. That's over 3000 albums with 50k songs. iTunes is great for ripping CDs so I'd recommend that regardless of where you upload to, and unless you're very confident about the existing rips you should do them again. You could then access your music library using either the Play Music or Apple Music app, and not worry about copying specific stuff.
Edit: And of course your music would then be secure and safe in the cloud.