On a wall you like as much as I do - I am sure - to see the frames aligned and not all at random.
I too - in general - prefer uniformity of frame sizes and orientations (but not always). That does not stop me from using different image proportions though. I use the frame mat to provide the consistency. I many times place horizontal images in vertical frames if that is what is pleasing to my eye with regards to the configuration of the frame. I absolutely love using very small 4x5 to maybe 6x8 prints matted out to quite large frames - and love using square format prints or proportions that are longer than normal to suit a crop that enhances the image.
One time when I put together a small exhibit - I had noticed other photographers just sticking up a mismatch of frame sizes and colors - - - and wanted a consistent elegant look even though I was using horizontal and vertical images and some prints that were not the same proportions as others. I think it worked well by worrying more about similarity of the frames than how the prints were cropped or positioned -
http://www.youtube.com/watch?v=sG8ptCJywmc&list=PLAC04A4B31C075FD5
However, when I make a portrait I photograph vertically with some exceptions of course.
Accordingly, landscaps are predominantly horizontal...
I know that when I started in the professional portrait business back in the late 1970's and 1980's - this was the common sentiment. However, I soon found works by photographers I admired that did not follow that ritual. Of course I had a strong inclination toward square prints at that time and sold much of my portrait work that way. Nothing stopped me from shooting and selling horizontal portraits and photographing landscapes in vertical format.
Same was said about pano shots always being horizontal. My studio walls displayed different vertical panos that were very pleasing to my eye.
I don't think it's necessarily what the images needs when it comes to cropping or orientation - I think those are as much the feelings and needs of the photographer at that point in time. Some other day, he/she may print the same image completely differently (as I did many times being I processed all of my own work).
That said - we each have out own preferences and those need to be respected. I do respect your viewpoint.
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