When I lead trips I was a dictator. I made the group ALWAYS stay together. If one person slowed down, we all slowed down. I never lost anyone. I usually limited trips to 6 participant.

Of course, when leading courses for NOLS, we had three instructors and 17 students. First week we hiked together, teaching skills along the way, not too intent on actually making miles. Then we split the students into 4-person groups and they had to go on their own. They had to submit a travel plan and one student was designated leader. They were strictly prohibited from splitting up. We instructors would stealth hike behind them, sneak through the trees and observe their actions, and get to camp before the groups. If every one were not accounted for, we then did a search and rescue.
Any group could only go as fast as the slowest member. If you wanted to go faster, you simply had to distribute the slow person's gear among the stronger hikers.

Even now, although I mostly go solo, if someone goes with me, we stick together. Why even go with someone if you are not going to stick together?