The title says it all. Every field table in database has exact same content as its revision table. My field_data_body table is 18.4MB large, so is field_revision_body. And the data inside is identical. I don't have a single revision on my website so why would there be a redundant information in the tables. As the database grows this will only add to overhead. Is there a reason for theses tables to hold duplicate data? Is is safe to empty these revision tables?