Jason Miller, over on his blog, just asked why all the ritual outlines we see tend to start with LBRP or LBRH, and not the Opening by Watchtower, when doing practical magic in the Golden Dawn/Modern Magick context.
(For the sure-to-stumble-upon-this-post newbie: LBRP---Lesser Ritual of the Pentagram; LBRH---Lesser Ritual of the Hexagram; Modern Magick is the title of a book by Donald Michael Kraig, which has became the core textbook for a lot of people.)
I am not sure that I have a good answer for him. For that matter, I am not sure if I am in the context that he is talking about. I presume that I am. If not, *shrugs*.
So here is my personal answer, I generally skip the LBRP and LBRH in my own workspace; it is used for lodge and ritual related work mainly, so I only occasionally have to clean up after a non-ritual use. But I teach that if your ritual room is used for something else, then one really should do the Lesser Rituals of Banishment.
(The use of the room by the cats do not count...though occasionally I do wonder what they are doing with the simple Enochian Chess set.)
And most of my rituals start with the proper Opening of the Grade that I am working in. The kicker is that the Opening by Watchtower is not part of any of the Golden Dawn Openings that my Order uses. Therefore, I do not spend a lot of time working with it. (There is Enochian in the Openings, but not this particular ritual.)
As for the greater Golden Dawn/Ritual Magick community not using the Opening by Watchtower more often, I would venture the guess that they are taking their cue from what they see other people doing. Given the fact that most are learning from reading books and other material, it is natural for them to think of this as the proper way of doing things. If you see a hundred outlines saying that the Lesser Rituals of the Pentagram and Hexagram is the proper way to start, and only one that says otherwise, you tend to go with the majority opinion.
I learned practical magic by observing actual people doing the work, therefore I picked up a different set of habits. Of course, one wonders how the people who showed me Our Arte and Craft overlooked the fact that most of the Regardie examples start off with the Lesser Rituals of Banishment. Then again, one wonders how the Modern Magick community have ignored Kraig's examples. I know the answer to the former, but not the latter.
If you have a better answer than mine, please hop over to Jason Miller's blog and tell it to him.