At the moment i buy discs for single-player games, or ones which may become "classics" and i may want to revisit sometime in the future; digital for multiplayer (or mostly MP only) where the game will be dead once the servers are turned off.
Sure digital has nominal better convenience (i remember before TV's had remotes, and you had to walk over to it to change channel!
pffft millennials), but at the mo digital may not be cheaper and you're at the mercy of companies that gimp a game through either patches or server uptime.
At least with a disc i can put it in and play the day-one
(or technically pre-day one) version, and i
own the game, digital and you're basically
renting something at full price.
For newer ED players, David Braben (OBE) said way back:
"We have no intention of taking the servers down, but I understand what you are getting at. We plan to archive the game from time to time (ie matching client and servers and game world state), and would release such an archive if the servers were to come down. That would also address the issue of how you preserve an online game for the future, from the whole 'retro' perspective."
Of course who knows if they'll honour that, a lot of desgin commitee stuff hasn't happened, but there's a slim chance an offline ED would be available when the servers go.
https://forums.frontier.co.uk/showthread.php?t=60284&page=14&p=1024593&highlight=#post1024593