People who use focus groups sometimes go to great lengths to stop respondents from influencing each other. This ironically removes several of the benefits of groups that are all based on social interaction! You need to understand the benefits of both depths and groups and make sure you don’t throw the baby out with the bathwater.
One of the skills of moderating is to foster interaction between the members of the group. A group should be more than the sum of its parts. A good moderator knows when the group is running with the topic and does not interfere. There is a difference between moderating and controlling.
Hint: if you are doing groups because you need to interview a number of people quickly but don’t need/can’t afford depths – try using a bulletin board.