I have read all the posts in this thread. It is amazing how it wanders.
To get back on topic: in the past 8 years I accumulated a wide range of Zuiko lenses. The range goes from 18mm to 500mm.
There's four variations of the 50mm focal length in the accumulation (50/1.4, 50/1.8, 50/2 macro, and 50/3.5 macro). There are also the 24/3.5 shift and the 35/2.8 shift lenses, which can be used as normal lenses, but that's not what they were made for.
If I told you I picked a 50mm lens, I would also have to say which one of the four, because they have distinct uses, or properties of size and weight. Likewise with the shift lenses.
When I go for a photo hunt (wandering until I see a good opportunity), I pick a lens that suits my mood at the time, or which I just want to try out some more, and then look for subjects that meet that lens' field of view. I often revisit sites where I have taken pictures at a different focal length and see what other kind of photograph I can make with the current focal length.
Consistency is not my watch-word. I try new things all the time. Thus I have close-ups and distant 18mm pictures of the same park bench under an oak tree at the park. The same subject, very different pictures, and very different moods, all inspired by what the lens could do.
For macro photography, the focal length all depends on how far away from the subject the lens needs to be. For that I have 50mm, 90mm, and 135mm. Trying to get insects in their natural environment with a 50mm is not very workable, since the lens has to be so close, so I use the 135mm for that task (and I am not very good at it, yet).
To do more-or-less formal portraits, I have found that the Zuiko 90mm f/2 lens is far, far better than any of my other lenses, even other brands. At one sitting, I just could not get a decent portrait of my daughter using a Canon 24-105mm zoom lens using a Canon digital camera. I put on the Zuiko 90/2, via an adapter bought from the head bartender here, and the portraits were just beautiful. So saying I use 90mm for portraits wouldn't tell the whole story for that either.
When I have a specific task to do, I follow the general rules I have learned from books, magazines, and the internet on what focal length (and other property) best fits that task.
When I am free to find any subject at all, then I depend on inspiration from the focal length that I chose to use on an outing, and look at the world differently, to match the lens.
I find that rewarding, and even occasionally get a good picture.