I have taken many rides with groups. It can be a hassle. I really do not like the staggered configuration. Too crowded, too many bikes to watch.
I rode in Greece with a group. They do not ride staggered. Just single file and stay to the right. This seems to be very good. the fast riders would be in a group ahead and the slower guys would be in another group. Rather than watching out for the other bikes and trying to keep up, it was much easier for us to look out for each other. Staggering double file in one lane is some 'B' movie biker crap, I hate it and do not ride like that even if the I am with a group that does