If my response seemed uncivil, I apologize. You asked a simple question and I offered two short, simple opinions from the perspectives your question covered, aikido and fighting. I'm sorry if it came off any other way.
No worries. Sometimes "tone" is lost in text.
In terms of all the big names giving that direction to spread fingers, and all the video showing them doing it, I don't dispute it. But what I have yet to hear is WHY (emphasis, not yelling) they do/say it. I know it is not very "Japanese" to ask "why" when given direction, but I'm not Japanese..... What I am is a scientist/engineer looking for a solid mechanical explanation. The only one I have heard given (not on this thread) is that it increases the diameter of your wrist and somehow this creates a better/more advantageous connection with uke when grabbed. I've experimented with this and it doesn't hold water for me. Perhaps someone can elaborate...