I believe the most important statistics to keep and track are the number of cell groups and how many people are in those cell groups each week. Secondarily, but just as important, is knowing how many potential new leaders are currently being equipped to open a new cell group and what step they are on in the equipping track. Complete reporting in these areas is vital to accuracy; each cell MUST report every week without exception. The most important activity of the cell champion, cell supervisor or whoever collects and compiles the statistics is obtaining the reports from the leaders.
Keeping a record of Celebration attendance is only needed to compare how well you are moving people from the large weekly meeting into the small group gatherings. For example: if I have 10 cells and my weekly reports from leaders tell me there were 80 people in cell meetings last week and there are 120 people in the celebration, then I know there are at least 40 more possible new cell members waiting to be assimilated. This leads me to the conclusion that I need at least 4 new cell leaders soon (if the existing 10 cells cannot accommodate the average of 4 new persons each). Certainly this is an example, not a rigid mathematical suggestion. Statistics gathered must serve us, not us them.