I think it’s primarily done for layout matching. As long as your schematic is readable, doesn’t violate pdk requirements, meets specifications, and matches your layout, it doesn’t matter too much what you do with your devices from a schematic point of view. Ultimately the layout is what gets fabricated. The only other thing I’ll say on odd fingers, is that there may be some instances where you won’t be able to create clean ratios. For example, if your current mirror has 3 fingers and you want to mirror half the current to another branch, you can’t create a 1.5 finger device.