lightroom Desktop photos same as lightroom classic

With cloud Lightroom desktop, it’s OK to start editing whenever you want. For example, if you import 100 photos, they are first all temporarily stored on your device while they wait to be synced up, so there’s no problem starting to work on them. An image might start uploading while you’re working on it, but that’s OK, you probably won’t notice because Lightroom will keep track of where it is.

As far as reliability with Lightroom vs Lightroom Classic, as with many things in life…it depends.

Lightroom Classic always stores originals on your computer, so the availability of those photos in the future completely depends on the reliability of your own computer, its internal and external storage containing cataloged photos (will a drive fail?), and how well you maintain backups of your computer and its storage (if a drive with photos fails, is its backup up to date so you can recover everything from its backup to a new drive?).

Cloud Lightroom always stores originals on Adobe servers, so the availability depends on how well Adobe maintains those servers, and they should be expected to do a good job. Most reputable cloud services (Adobe, Google, Microsoft, Apple, Amazon…) maintain copies of files at different locations, so if a disaster destroys one server location, a server in another region will have the same files and can take over instantly, so you never notice that there was a problem. So, some cloud service companies do a better job of redundantly protecting data than many of us do.

Cloud Lightroom availability also depends on continuing to pay the subscription fee for the amount of storage you need for all your photos. The last time I checked, Adobe says Lightroom photos in the cloud are available for you to download for up to one year after cancelling an account, although that might change. If you ever want to cancel the subscription, you can use the free Lightroom Downloader app to download a copy of every Lightroom photo you have in the cloud, so that you have them on your own computer after you cancel the service.

Photos that you EXPORT to your hard-drive are the same for exports from either Lightroom or Lightroom-Classic. (The file-type is your choice, of course. JPG,TIF, etc)

The two apps (Lr & LrC) do store your original files differently.  Lr uses Cloud storage. LrC stores you files locally (on your hard-drive system).

Mega-byte size of files has no relevance to file quality, but using anything that compresses a file smaller (eg.JPG) will reduce quality.

"Reliability" is your responsibility to keep your files and computer system in excellent 'condition' as well as keeping reliable backups of catalog and original files.