Thanks for the kudos about our previous discussion. I'm glad we've been able to help out a bit.
Unfortunately, it's next to impossible to guess why someone recommended something without knowing the entire context of that discussion, so probably your best bet would be to go back and ask the person who made that suggestion.
If, for some reason, that's impossible (eg, you were chatting with person at a trade show and you didn't get his card), my 1st guess would have been the same as besmirched: smooth dreamy backgrounds (aka, "good bokeh" vs the typically harsher bokeh one gets with kit zooms).
There are a few other possibilities:
1. (so obvious it's silly) - For some reason, that person misunderstood your needs and thought you were interested in macro shots.
2. Macro lenses are usually short telephotos, and the conventional wisdom is that head shots and head-and-shoulder portraits are best done with short teles. The reason is that if you use a "normal" FL lens, you'll have to move in to about half the distance to fill the frame with the subject. The resulting perspective can exaggerate noses and other facial features. When you are that close, if the subject in a head shot is looking straight at the camera, you may be so close you don't even see their ears (because they are hidden behind their cheeks, etc. Think of how most cell phone "selfies" look. Much of that look is the result of shooting too close because the FL of the lens in the cell phone is too short. Another reason people don't want to get so close is because it some subjects aren't used to having a camera that close to them and it makes them nervious. In contrast, if you go to much longer focal lengths, the working distance goes way up. You may not be able to move that far back in a small studio, and shooting from that far away tends to foreshorten people's faces, reducing the apparent depth of the face by too large a factor.
3. The acceptance angle of short telephoto lenses is less than that of more normal focal length lenses. In a small, impromptu studio, this makes it much easier to exclude things in the room (eg, wall not covered with backdrop material, etc.) that might be visible at the edges of the frame, even if you move in close. The smaller acceptance angle of longer FL lenses also allows one to shoot between closely spaced lights, softboxes, etc. without getting them in the picture. The smaller acceptance angle also allows one to use a long lens hood to prevent off-axis stray light from directly hitting the front element of your lens.
4. For a given price, a short telephoto / macro tends to be of simpler design AND better optical quality than a similarly priced kit zoom.
However, even after listing the above possibilities, if I recall your previous question, you have a kit zoom lens that you can set to short tele focal lengths, so you already have points #2 and #3 covered.
HTH,
Tom
PS - FWIW, ever since I started doing serious photography in the mid 1960's, I have used short tele lenses for many of my portraits. They just "work" for me and many other photographers.
PS#2 - Note that I've been careful to distinguish short telephoto, single focal length lenses from "macro" lenses. The reason is that (a) not all macro lenses are short telephotos, and (b) some people feel that in the region of best focus, macros are *too* sharp for portrait applications.
