[Xbox One] Digital download from disc.

You have names mixed up. There are no consoles named the Xbox One Series S or Xbox One Series X.

The Xbox One/One S/One X all have a disc drive.

The Xbox One S All Digital Edition does not have a disc drive.

The Xbox Series X has a disc drive.

The Xbox Series S does not have a disc drive.

All the consoles can play backward compatible games. The Series S and One S all digital edition can only play games digitally downloaded.

The other consoles can play games from disc and from digitally downloaded,

I hope this clears things up for you.

On the Xbox One, digital and physical disc games are one and the same. The data you're usually downloading is just packed on the disc. The disc is only replacing the download, as the game data is copied from the disc to your internal harddrive anyways.

However, when you get a physical disc, the disc is the digital license (something like a "Proof of Purchase"), and has to be in the drive when you want to play the game, even if it's run off the harddrive.

On the other hand: If your disc is damaged, but the security sector with the license is still readable, you can insert the disc, and download the download version from the store. But you still need the disc to "unlock" the download.

BC games do not install from the disc, but are downloaded digitally from the store.

Is this a disc or previous digital download for the 360?

Specific to Xbox One, Digital allows for play without a disc present. It prohibits resale. Games purchased digitally can often times be refunded with a call to Live Support. I did this for the Xbox One version of the Destiny Digital Guardian Edition after
the news came out about the buy on 360, get it on Xbox One for free.

Disc-based games must have the disc in the console to be played. They can be resold. Disc-based games routinely go on sale unlike Digital, though MS has been better about sales on digital titles as of late.

There is no "size" difference as both digital and disc titles deposit the same bits on to the Xbox One HDD. In fact, installed-from-disc titles can be converted to digital titles (and thus obviate the need for the disc) by simply buying the digital version
of an installed-from-disc title. No re-downloading is required.

One thing I 4got, and it's very important...sharing ur games like this only works if u originally bought the game in digital form. I.e. From the xbox or MS store to download. Disc based games won't work for this...as ull need a disc for each box u have.
With digital downloads, they transfer from one box to another...