This is not warning, but required action because LR Classic work with new/updated format of catalogs. And AFAIK you can't avoid this action and skip the step. You can continue to use LR 2015 with old format of catalog. But if you need LR Classic you must migrate the catalog.
And you can migrate only once because after the migration the catalog will be in ...
Lightroom Classic CC is already behaving that way. A few important things to note:
You can only ever set up one catalogue to sync with Lightroom CC
It won't sync the full catalogue, you need to specify collections which you want to sync
The synced smart previews don't count towards the cloud storage usage, only full-resolution images do
If you import ...
I prefer to use Capture One. I find the catalog feature is better than Lightroom. It is also a bit faster, and you can work with layers in Capture One, which Lightroom.
The focus mask tool and loupe tools are awesome for checking out image quality, even in grid view mode. It is more expensive though. But in my opinion, it is worth it.
I have written an in-...