It is very beneficial to both the reader and the author of a document if all tables, charts, illustrations, diagrams and pictures are numbered.
Numbering makes it possible for the author to easily refer the reader to a table, chart, diagram or other graphical element, no matter where the reader may be in the document.
Numbering also helps the reader to quickly identify which graphical element they must look at.
See example below.
Numbering may be achieved in two ways - manually or automatically.
Manual numbering is simple for the author but errors can be easily made. Revisions of the document may alter the order in which graphical elements appear and numbering needs to be re-adjusted. It would be a cardinal sin for the reader to be referred to the wrong diagram because the author forgot to check the numbering,
Automatic number can be achieved to remove the possibility of incorrect numbering by using the SEQ field but this requires technical skills beyond the average user. It takes much time to learn how to insert fields into a document including the SEQ field and this would detract severely from the time allowed for writing the document. If you are interesting in learning how to use the SEQ field, pick a time when you have many hours to spare. Once learned, though, the ability to use automatic numbering in your document including the PAGEREF field has a long lasting benefit.