I've discovered that Lightroom CC (after migration of my 'classic' catalog, put a catalog Lightroom Library.lrlibrary in my user/Pictures folder. It is more than 25 Gb and I really don't want it sitting on my laptop. I've copied it to an external drive. So, can I safely delete it from my laptop Pictures folder? Does Lightroom CC need to know where that catalog is? What's it for? I can't see how to set a location for this catalog in LR CC's preferences.
No, at this point in time, you can move the originals to another drive but the Lightroom Library has to be on the boot drive. Hopefully that'll become smarter in future. You might be able to get around it using a symlink, but that would be very unofficial.