Historical data is the record the auto-scheduler uses to look at past times your volutneers have served. This historical data is used to make sure that over time your volunteers are scheduled approximately the same number of times. It has no effect on any reports and will not remove any of your volunteers from past schedules.
You may want to clear the historical data if you recognize that certain volutneers (especially those who have served frequently in the past) are not getting scheduled very often, or if you notice some volunteers (especially brand new ones) are being scheduled too much.
You may not want to clear historical data if you have done it recently or if you are relying on that past data to keep volunteers from being scheduled too close to a past scheduled date.
If you are not sure if you should clear historical data or not, you can submit your data files (Help - Send Data Files to Tech Support) and tell us why you think you may need for them to be cleared. Please include the names of specific volunteers and the jobs that you are concerned about. We can then take a look at you and let you know if clearing the data will be helpful for that situation or not, and also recommend any settings that will help you achieve your goals in scheduling.