I'd imagine 99% of ChatGPT users see the app as the former. And then the rest know how to turn the memory off manually.

Either way, I think memory can be especially sneakily bad when trying to get creative outputs. If I have had multiple separate chats about a theme I'm exploring, I definitely don't want the model to have any sort of summary from those in context if I want a new angle on the whole thing. The opposite: I'd rather have 'random' topics only tangentially related, in order to add some sort of entropy in the outout.