First of all, you should have had a blank grid made up before the exam started.
While you "feel" this saved you time somehow, I just cannot figure out why. It's three columns (two vertical lines) and four rows (three vertical lines). Drawing them ahead of time squeezes your answer into a confined space and saves no time.
Actually, this last time around, I just did partial grids, with 2 vertical lines to separate the three different beer styles, then lined in the horizontal lines as I worked so that I could give sufficient space to each aspect of the question.
For me, having the grids partially prepared in advance serves as a memory aid and keeps me from being distracted (I have ADHD). It also saves a tiny amount of time and gives me something to do to calm my nerves before the test. (I have test anxiety, too.)
Other than that, your point is well taken. Grids should be minimal and should be an aid to formatting your answer and helping the graders.
I read in dummies about preping this and that and I tell my examinees to not number ANYTHING. I take time after the exam to have them number every sheet in a way which will be the same for all examinees who took that exam. Trust me, the graders like that.
This should be in the rules for proctoring the exam then, if it really does help.
There is only one piece of paper prep work I think examinees should do prior to the exam. Take a ruler and mark the margin 1" from all edges with a black magic marker. During the exam place that sheet under every sheet of paper you are using to take the exam and do no write outside that margin.
This is good advice. It's a variant of the suggestion to line out margins mentioned in "BJCP for Dummies", but is more time efficient, assuming that the paper you're given (usually a lined legal pad) is thin enough.
Again, this could be a standard thing that the proctor provides, since it would be easy enough to design and photocopy a blank 8' x 11.5" page with a big black border approximately 1" from the margins. Heck, you could incorporate it into the exam itself as the page before the cover sheet.