Some people can't look backwards as easily as others. Like me.

On the road as I head towards a place where I need to cross traffic to get left (left turn, or get past a right-turn-only lane), I continually monitor the traffic behind to see when a hole is coming up (or when is the end of the current 'cohort'). When it's time to turn, I do an extra actual look-behind.

Also, when I'm leading a group ride I can see the layout of who's behind me and who might be dropped. This is especially useful on trails (need to maintain attention forward), or when riding with kids in traffic.