When you know the enemy team is grouped and taking baron/dragon/elder and you can't contest it

You know they aren't somewhere else on the map or in position to respond. For a brief period of time you are free to move around the map uncontested, no matter how strong the enemy is.

This is an opportunity for your team to take vision control of something. The opposite epic monster if its up, the area in front of your base and your jungle if they took baron since they'll be sieging you soon, a side of the enemy jungle that you plan to send someone up to splitpush next to soon, key intersections on the map so you can see where the enemy is rotating early.

It's not dead time. Grab the vision while you have control of the map and you'll be in a position to mitigate the impact of that objective you just lost.