I use a tablet to casually browse (previously logged in under a 2nd account to test non-regular stuff when that mattered) but only ever this account for the UI. Very occasionally, for very specific reasons, I’ve started a print from it as well.
I have found that if you accidentally leave the UI open on a “second device”, it won’t overwrite changes if you ONLY click the ‘dashboard’ link. If you click anywhere in the workspace itself, it will save the design as it appears in that browser. It will also save that way if you just close the tab/browser. Only clicking on the ‘dashboard’ link prevents it - so that’s kind of a “don’t save” option.
It’s not exactly what you’re asking but I don’t know if it’s possible, because the changes aren’t only saved when you close the tab or go back to the dashboard - it’s updated pretty much in real time as you make changes.
I’ve tested that by having the dashboard open in two browsers, opening a design on one, making changes but not closing, then opening in the other - changes are reflected.
… then, on occasion, they aren’t! I’ve also had it where I could make changes in one, and the other, close both, open back up, and each reflected what I had done in the individual browsers.
I’d expect this is an edge case not really expected from a typical user.