The equipment tag is the one identifier that procedures, drawings, work orders and maintenance records all share, which makes it the natural way to link them together. When each of those is tagged consistently, a single piece of equipment becomes the place to find everything about it.
The hard part is usually cleaning up the tags, since different systems often use slightly different formats for the same equipment. Once that is done, you can also link qualifications to equipment types, so the system can show who is qualified to work on a given piece of equipment and which procedures they should use.