I don’t think anyone is suggesting that quantity over quality is the goal here. (Well, maybe some are, but they would be missing the point, in my opinion, or maybe they just work in a field I’d rather stay away from…)
Though time limited challenges and the like can serve as training to work in a more focused and structured manner, and to actually finish stuff at all, the goal is not to produce large volumes of mediocre work. The idea is to optimize your process and hone your skills, so you can work faster and more efficiently. If you can do that, you can of course leverage it to finish jobs in very short time (very important in trailer scoring, apparently), but more interestingly, you can also leverage it to get better results in any given time frame, or push the limits of what you can achieve when there’s no strict time limit.
Of course, if you already have years of classical training and professional experience, and/or an extremely good ear, maybe you already have all you need to realize your visions with perfection. If you’re a full time composer with no particular time pressure, I can certainly understand if adding a “stress factor” just seems pointless and counterproductive.
Personally, I’m an amateur with no classical training whatsoever, a full time job, and likely not enough years left to live to acquire the skill level I really want for my own satisfaction, let alone professional work, so I need to do what I can to make progress.
If I were already able to compose anything that comes to mind, and have it come out exactly as I intended it, I would just do that, and not bother with any of this. Is it even humanly possible to achieve that? All I know is, I’m nowhere near that yet, so I’ll keep doing a bit of this “basic training” for the time being.