A question I often get asked when I mention drill drawings is "why bother when the drill sizes are in the NC data" they say.
We bother because we concerned about accuracy, we are concerned that when the manufacturers are checking the data have something to enable them to do so. Inspection is not usually an automated task - it is done by hand/eye with spot checks on each size drill. If all they have to go off is the NC data then it is harder for the boards to be checked. If you ask a board manufacturer if the want a drill drawing I am sure that they will all say "yes".
Actually, the term "drill drawing" is rather outdated - now it should be referred to as a "manufacturing drawing" because if we want to be able to provide our board manufacturers with accurate information on the way we want our boards made then we need to give them some form of drawing etc detailing this with more than just drilling information on.
As well as what size drill goes where, if it is plated and how many there are we also provide other information such as:
Board type (FR4, CEM, ect), board finish (solder resist type and colour), plating, is it lead free HASL, ENIG, OSP, silver etc.
The board dimensions, any tab routing locations, Legend colour, ROSH compliance statement etc.
There is a lot more information that we can put into a drawing to tell the manufacturer exactly what we want in a board, and if you do not tell them this then it's your own fault if you get something back that is not what you wanted.
What if you have cutouts in your board shape - milled slots or holes, these need to be pointed out and in the one drawing is a good place to do it. When you do it in the drawing it easily becomes part of the standard set of documents output from your CAD system so you do not have to remember to go off and do it in a word doc etc.
I would not consider sending out Gerber's without also providing some manufacturing notes also as an RS274-X Gerber file.
(If it is also a Gerber then you can display it when checking your NC drill and Gerber data in a viewer to aid you (and your manufacturer) in your checking).
Not providing this information is like ordering a car without specifying what type, cc, colour or how many wheels it should have. Most times you'll get an OK car because your current supplier knows what you like to drive but change supplier and you may well end up with a pink three wheeler! (And I have had one of those myself.)