We have all heard the abbreviation T.M.I. For “too much information”. I coined another one N.E.I- "not enough information". I'll explain. In a shot course the instruction oftentimes becomes a compilation of disjointed tips and advice. Advice on more complex subjects is condensed or abridged for easy consumption and much of the underlying logic is omitted. OR- in such a short period if time, the “students” may not absorb everything even if all the and rhyme and reason is explained.
Some of the advice that the OP alluded does POSSIBLY make sense with further explanation.
I should mention that when I offer advice, I usually base it on what I do in my work, procedures that yield successful results and why they work. I do not advise on equipment, materials or methods that I have never had the opportunity to use or have no research knowledge of. I prefer to explain cretin basic theories with the hope that folks will apply the information and decide on things for themselves. And yes...there are alternative methods for just about everything.
So...If I am shooting a requirement for black and white photography, I do prefer to shoot it in monochromatic mode for a number of reasons. I can asses the contrast in terms of panchromatic rendition of different colors right on the spot and determine IF filtration is needed and how it should be employed. I realize that some photographers only relate the term “panchromatic” to film but it applies to a proper rendition of tones that can especially apply to portraiture in that you don't want to use a filter that, for example, lightens the skin tone but renders the subjects blue eyes as almost white.
By the way- there is no use in telling folks to go back to film unless they have a working analog darkroom or access to good processing and printing facilities. It is doubtful that newcomers to our craft are gonna go there. Absolutely excellent black and white photography can be achieved with modern digital equipment and a bit of artistic and technical savvy.
If I want to make color images on the same job, I can switch back and fortr or use two cameras.
Oftentimes on commercial shoots, the art director or stylists are working with me so I can tether the camera to a laptop and we can see the monochromatic results right on the spot. We can make decisions, revisions there and then and make certain the client will be pleased and that we will meet the deadline.
Usually, I like to approach black and white work on it's own merits and criteria rather than decide to go monochromatic as an afterthought or a remedial action for a bad color shot. Yes- sometimes I have to do that but it is not my favorite method. When shooting monochrome, I am more concerned with line, texture and tones and I don't want to be “fooled” by pretty or contrasting colors.
Unless I am mistaken, I don't believe that good rendition of highlights, middle tones and shadows or inclusion of all the “zones” is solely dependent on post procession manipulations as long as exposure, dynamic range, lighting ratio and all contrast consideration are properly addressed in shooting.
I am certain that good black and white results can be obtained BOTH in the camera or in post-processing as long as the photographer has comprehension of panchromatic rendition, orthochromatic rendition and how colors of various hews and densities relate to the gray scale.
As for MANUAL operation in portraiture, there is some sense to that method. In both a studio, location, or out of doors environments, the photographer needs to maintain exacting control over exposure, lighting ratio for key and contrast, depth of field as to inclusion or blurring of background detail and artistic consideration such as “bokeh” etc. Selection of ISO settings, shutter speeds and aperture settings have to be selected accordingly. In a strictly studio setting, where the photographer is completely in control of lightning placement, most portraitists have standardized setting for the various kinds of work that they produce. In all of theses scenarios, manual settings are more conducive to theses requirements, procedures and methodologies. Even basic exposure readings need to be sampled from the right “zone” on the subject and integrated or matrix readings would not yield the best results. If any automation is used, perhaps aperture priority might be a good choice in existing light situations.
Frankly, I have been to many workshops, seminars, classes and lectures and SOMETIMES, I learned how NOT to do things or present a seminar. That's why I never asked for a refund - everything can result in a learning experience. Mostly, all of my mentors, teachers and instructors were great. I consider myself a fast study, a quick learner, I take good notes, I listen up, I ask questions and participate and do my homework and yet- I have gone back to a few of my best teacher's classes multiple times. Good teachers can get into incredible detail, drill down deeply and dispense megatons of information. We are all human, we are not audio or video recorders or computers and everyone has a saturation point.
Some concepts can not be fully explained in quick tips. That's why I write long verbose posts. I was so busy learning photography that I did poorly in English class and totally neglected typing class so excuse the bad grammar and typos.