In my study and experience in this area, I've found that the growth of a church is limited by the ability of the church to assimilate new members into areas of ministry and the ability off the church to care for its members.
If folks are feeling either under or over utilized, they will sooner or later begin looking at the back door. Likewise, if folks begin to recognize that no one really cares for them (outside of the committee nominating period, the January stewardship sermon series, or during the capital campaign), they will, sooner or later, be looking to move on or drop out.
Think about the maximum number of friends with which you can maintain intimate relationships. I have hundreds of acquaintances and friends (I am still smarting over the postage bill for all of those Christmas cards this year
but I am able to maintian intimate ties to only about 7-10 at a time (I am a layman, work 45-60 hours per week, travel frequently for business, have a family with two children, etc...).
It would seem prudent, then, to make sure that each member of one's church is a member of a group of 7-10 persons. As new members are added, groups increase and divide.
Two cool things happen when this is done: members are cared for, and lay leaders emerge (some even enter occupational ministry).
Not a bad plan for growth.