Yesterday night I messed around with the "using only one move in neutral" idea with some friends and I actually found some pretty interesting things.
First of all, limiting yourself to just using upair and grab really does show how limited you become and how out of the box you have to think in order to do those two moves. There were several occasions where I got a grab on my opponent but he DIed and tech-ed behind me and I thought "dang, I could probably bair there." Most of the time I would use my upair to just try to hit my opponent and I rarely used grab or tried to bait him into shield to use grab on him. Using only upair meant that I had to do a lot of retreating upairs in neutral, I got to practice tipman edgeguards a lot, and I also worked more on doing the instant upair to try to hit Fox on the ground, and even that was hard to do on command in friendlies. But it definitely does show you the potential of upair, and how it can be applied in many situations. But using only upair, you get to see all that upair has to offer, in ways that you already knew, and in new ways that you might discover (like hitting Fox with the tipman on stage in neutral when he tries to jump in on me). You get to see where upair is strong as well where upair is weak. It's weak when you are facing away from your opponent and you want to come down and try to hit them with a strong move, so instead it's probably better to fade away from your opponent and upair so that it covers the space behind you when you land, making it safer to land.
Soon enough I slowly incorporated more moves into my gameplay and it was like building the blocks to the house of Ganon haha. It almost came with new knowledge or an expansion of knowledge I already knew about the character. I definitely feel like this is worthwhile in friendlies, because forcing yourself to use only one move means you are able to point out your habits more and see if those are good habits or bad habits. For example, a habit I would have is to dair out of shield on reaction to a certain attack on my shield, or a bair in neutral when my opponent is in a particular position. I would point out to my friend that the bair or dair I just did was completely a "knee-jerk reaction" and probably a habit. Now with that in mind, using one move can also expose your bad habits. I would often try to come down and hit my opponent with bair in mind, but since I was consciously limiting myself with upair, I would get hit a lot by spacie uptilt, something that I wasn't too aware of before last night.
I feel like it's small challenges like this in friendlies that are beneficial to learning more about the game and about your character. I did the same thing last night using only Link's nair and grab and got a lot of similar results, as well as understanding more about how Link's nair actually works. Now, I don't recommend you use this for every move the character can use. You want to use moves that have multiple uses and see if you can discover more, cause it's pretty useless to be Ganon and just try to side-b your opponent all the time. Using only one move in friendlies is actually kind of fun because it presents a challenge to you by purposefully limiting yourself. I believe it can help you learn more and I encourage people to try it out more in friendlies.
Oh also, when playing Puff, if she bairs your shield and is doing wall of pains, if you do an instant fair out of shield while holding forward, there is a very good chance that Ganon will at least trade with the next bair that Puff puts out. There are definitely some nice situations in neutral against Puff where putting out a fair early to challenge her space ended up paying off and getting me stage control. You do have to be a bit pre-emptive against Puff, but if you know what she is try to go for in neutral, your big hitboxes will straight up beat or trade with hers, and she hates trading. You just gotta do it early enough and be safe about it when you do it.
