"I am not among those who decry statistics, nor do I consider that they are productive of all manner of evil; for they do much good if they are accurate, and if men use them lawfully. It is a good thing for people to see the nakedness of the land through statistics of decrease, that they may be driven on their knees before the Lord to seek prosperity; and, on the other hand, it is by no means an evil thing for workers to be encouraged by having some account of results set before them. I should be
very sorry if the practice of adding up, and deducting, and giving in the net result were to be abandoned, for it must be right to know our numerical condition. It has been noticed that those who object to the process are often brethren whose unsatisfactory reports should somewhat humiliate them...."
"The fact is, you canreckon very correctly if the figures are honest, and if all circumstances are taken into consideration if there is no increase, you may calculate with considerable accuracy that there is not much being done; and if there is a clear decrease among a growing population, you may reckon that the prayers of the people and the preaching of the minister are not of the most powerful kind."
Spurgeon goes on to talk about the importance of making sure we are doing our best to count new disciples being added to our numbers and not just those who get whipped up into a frenzy and say "yes"out of sheer emotion but not truly understanding and responding to the Gospel in faith.
Taken from "The Soulwinner" in the chapter "What it means to win a soul."
From my perspective it's fine to track attendance numbers in church/youth group but we should get WAY more exicted about new disciples being made and multiplied in our midst. For more on this check out value #6 on gospeladvancing.com