While you are actively working with your data, you generally have a very clear idea of what information each file contains, the part of the world in which the information was collected, how the information was collected and subsequently altered, and major strengths and weaknesses of the data source. As soon as you stop actively working with the data, however, it is likely that these details will fade from your memory. Clear documentation about the data, created while you are working with it and while it is clear in your mind, thus helps both the data creator and future users understand how the data has been created and the processing undertaken on the data.
The other reason to document your data is to help others. Some form of record about your data is generally useful for close colleagues and others working in your organisation. More importantly, documentation is critical in order to create a lasting archive of your work that is useful to others. Archive users will have no way of knowing anything at all about your data unless you tell them. Reasons for archiving data are discussed further in What is Digital Archiving?.
4.1.1 Types of Documentation
In documenting digital resources it is possible to go into great detail and record everything, from characteristics of the source data to the mathematical algorithms which were used to process individual images. As with most things, the appropriate level of detail depends on the likely uses for the documentation. For the purposes of this Guide we have thought carefully about the level of documentation appropriate for digital resources created by archaeologists from aerial photographs or remotely sensed data. Some types of documentation seem absolutely 'essential' while other types of documentation are only 'recommended'. Don't let this limit you, though, this is one instance when 'more' means 'better'.