My experience acording to the standard and the 45 degrees viewfinider is that the image appears larger and brighter in the 45 degrees viewfinter. It is much easier to control lines, composition and focal plane. If you prefer a horizontal trim / diving style, you will also find it easier to look trough the viewfinder. At least my neck feels better with the 45 degrees viewfinder than without. Anyway it is fully possible to make beautiful photos with a standard viewfinder and i still make awful photos with one.
I thinkk the attached image might be my favourite from 2014. Not becauce of the quality, but because it was the beginning of thinking repeating shapes when I'm working with the smallest subjects. Lens: 100 mm with 2 extention tubes + 10x diopter. Full frame. .