I am looking for some best practices regarding forecasting.

  We are creating a detail forecast and then summarizing based on company, large customer and a category code on the item.  We have multiple people updating forecasts (sales people update their forecasts) so we are not sure when a forecast changes.  Should we run the force change program daily and just pick up anything with that day's update date?  Also, we summarize the forecasts monthly for the next 12 months (and would like to go out even further).  If we add a new large customer, or a new item to an existing customer, can we run the Summary program