What the problem here is for your question is Mark's video is confusing. Normally when you do a balance staff you would statically poise first then sometimes dynamically poise. If your dynamic poising you use eight pendant positions usually. So in his video he comments for this particular watch he is dynamic poising.
Then adjusting to positions is an interesting term or as your question is which positions should you worry about timekeeping in? Basically what you're doing by timing the watch on the timing machine in a variety of positions is your verifying the watch does keep time in those positions.
So for pocket watches dial up and crown up are the most common.
For wristwatches I'm attaching what Omega recommends for their watches
check each as old hippy said but end shakes on a 3rd wheel allow a lot more play than lets say a balance or escape. you can get away with too much end shake and not loose much amplitude, too little will def not work though and will def result in a very low amp and or stop the movement. train wheels being loose is always better than too tight in my opinion
its farfo.com dont put the www. or just google farfo vintage watches ridgewood nj. archer is a memeber on teh Watchuseek forums and is very good esp when it comes to high end watches like omega. he is a certified omega repairer, not many of those around. he uses the same equipment they uses at the omega facilities. 100,000s worth of equipment