I use it as a DM. As mentioned above, it is great for creating pre-gens. I run an AL style game where drop ins are always a possibility, so I need to keep some pregen’s available.
I use it for prep: I’m running TOA in an in person game. My DM in a play by post turned on content sharing, and they have TOA in DDB, so I’ve benefited enormously from that. (I have access to TOA in print, too). I’ve printed off maps, NPC stats, etc.
At the table, I have it up on my iPad (in safari), usually in several tabs, so I can search monsters, spells, etc. If I know a particular monster or encounter is forthcoming, I pull that creature up in a tab.
I also use it to store some of my characters, including the one I use as a DMPC if I only have 2 players on a given night.
Right now I don’t have a subscription and have only purchased the PHB plus a race and subclass from other resources. I have access to the DMG, MM, Volos, XGTE, and TOA thanks to content sharing. Which has been wonderful.
I’m thinking about using Christmas money to purchase a hero tier subscription as I’m finding the 6 character limit rather stifling.