I can’t find anything about clipboards anywhere, so i guess I’ll ask.
In my mind, different clipboards would be for having multiple projects open at the same time, without having to open separate instances of renoise. Clearly this isn’t the case, so what is the point of clipboards and how do I use them?
You can store different pattern data parts underneath different clipboards. Or perhaps you want to move pattern data and store a copied automation pattern underneath a different clipboard. (you can’t copy a track selection and automation selection at the same time)
The lack of a good visual cue which clipboard contains what makes it a bit risky to use… you must use a certain tactic each time that you use them to prevent overwriting unwanted areas or erasing clipboard data that you still wanted to use…
I totally forgot about clipboards!!
That would have saved me a bunch of time the other night.
I honestly thought they “vanished”. 
press alt-1 then select area,
copy,
press alt-2 then select new area,
copy,
go to your intended testing destination where you want to paste the first data you copied.
press alt-1 and paste. you will be pasting the data from clipboard 1
now if you press alt-2, you will be pasting the data from clipboard 2.
very handy.
Makes me wonder why there is no info about clipboard used in notification area, where I naturally first will be looking for it.