Group riding gets a mixed reputation. It's often blamed when something goes wrong, usually because the thing that went wrong was a group riding badly, not group riding itself. Done properly, riding with a crew measurably helps.
Staggered, not side by side
The formation most riding safety organizations teach is staggered: riders alternate between the left and right third of the lane, roughly one second behind the rider diagonally ahead, and about two seconds behind the next rider directly in their own track. It looks casual from the outside, but it's doing real work, giving every rider a clear sightline and enough room to react without being boxed in.
Riding directly side by side removes that room entirely. If either rider needs to swerve, there's nowhere to go.
More eyes, faster response
A crew collectively notices hazards sooner than a solo rider does, debris, a merging car, a change in road surface. And if someone does go down, help and a hazard warning for the riders behind arrive in seconds, not however long it takes another road user to notice and stop.
The part that actually causes most problems
It's rarely the group itself. It's a newer or less confident rider trying to keep pace with riders above their comfort level, because nobody wants to be the one holding things up. The fix is simple and worth saying out loud before every ride: everyone rides to their own ability, and the group's pace is set by its newest rider, not its fastest.
See where your crew is riding and log group rides together in Crew, so the whole ride is on record, not just your own leg of it.