Is it necessary to migrate every single document or are some no longer required?
Do we need to bring all versions of a document across, or only the latest versions?
What are the retrieval patterns for those documents? If documents are only accessed during the first 6 months following creation, do we only migrate the latest 6 months and archive the rest?
Duplicates often exist. Do we need those too?
Do we understand what we are migrating? There are tools to help us analyze file shares in order to get a feel for the sizes and types of documents.
File shares may contain programming scripts, database files, large zip files, huge bitmaps and videos, as well as corrupt files. Can we leave some of these behind?