In cell churches, discipleship comes from the equipping track and the care structure for those who are leading cell groups. I would say that cell groups are leader breeders. You need to get them in, but also to move them out. Make sure the cell groups have a focus on cell multiplication. A danger can be on the focus too much on themselves.
Healthy groups can stagnate.
Make sure the groups are multiplying. New leaders do need to be trained. Most churches have equipping tracks in place. The mother cell leader would need to supervise a new leader. People will not lead small groups until they are presently participating in their small groups.