Cloud Storage or back up

How the Lightroom Photos cloud storage is used depends on which version of Lightroom you're using on the desktop. And neither of them is a backup.

If you use Lightroom Classic, you can sync specific Collections (which you must manually set up) to Lightroom Photos cloud storage. But this is not a backup, because only Smart Previews of your originals are synced to Lightroom Photos. With Lightroom Classic, if you want a backup of your original photos, you must set it up yourself, independently of Lightroom. You could sign up with a cloud backup service such as Backblaze and point it to where your photos are.

If you use Lightroom, then the master set of original images is in Lightroom Photos cloud storage, with your devices only storing temporary local caches of the cloud-based masters as you edit. Because your originals are in the cloud, by definition that is not a backup. Adobe is presumably keeping its own distributed CDN backups of everybody's photos, as any cloud storage provider would, just to ensure maximum uptime and no lost data. And you can retrieve deleted images for a period of time. But if you want local or cloud backups that you can access yourself, once again you'd have to set that up yourself. That requires setting up Lightroom in just the right way so it will keep a local copy of all your cloud originals, then you'd set up your own local or cloud backup that points to that local store.

Either way, the purpose of Lightroom Photos cloud storage is to let you get to your images from multiple devices over the Internet, not as a backup solution.

It's also worth mentioning that Lightroom Photos cloud storage is unrelated to, separate from, and cannot be viewed from, Photoshop Cloud Documents, Creative Cloud Files online storage, Creative Cloud Libraries, or Adobe Document Cloud.

Since Adobe added the Deleted Items section, it keeps your deleted files for 60 days so you can restore them and recover from accidents. It is an important safeguard, but just like trash or recycle bins aren't backup, neither is this Deleted Items.

Yeah, it really isn't a very sound idea to just upload images to Lightroom for the cloud and then rely solely on Adobe to be the archive of precious images. Literally anything can go wrong. There needs to be another backup somewhere, either on a local hard drive (internal or external) or another cloud service.

If you've only got one copy of a file, wherever, you've not got any backup. So:

1. Importing files to Cloudy Lightroom isn't backup unless you have a separate, independent copy of the file
2. The preference to save a copy of your computer is not backup, it's a local cache. Deleting that photo in Cloudy Lightroom will also delete the local copy

If your pictures are important to you, you should make a copy somewhere when they go into Cloudy Lightroom. That might be another cloud service or it might be on a hard drive.

If you are going to be using Lightroom (for the cloud) then your images are stored in the cloud. One of the options you can choose in the preferences is to save a copy on your computer. But the main thrust of that program is to have the master images stored in the cloud. The purpose for doing that is those images can then be accessed on other devices (mobile phones, iPads, etc.) on which you choose to install the Lightroom mobile application. And photos taken on those devices can be synchronized back to your computer.