It depends how you want to play. I think having rules does help you execute your team vision and generally is helpful, if you know what you are doing. I know some experienced players have 0 rules and do just fine adjusting the general gameplan every game. But if you want specific things, like "go for it on 4th and 1" or special short yardage defenses, or whatever, the rules give you that level of control. I'm not sure they make a huge difference from using the general game plan, but at least you feel like you have more control. You don't have to scratch your head and wonder "why did CPU coach call that play?" You get more influence over that - like you can say every 4th and 1 you will run. When you play against the top top owners, even little things on the margins can be the difference between winning and losing. But be careful setting them up - many a tale has been told about "I screwed up my rules by accident and I was going for it on 4th and 20 from my own 10 yard line" or stuff like that.

Here is one such forum topic if you haven't already seen it:

https://moguls.myfootballnow.com/community/3/7509?page=1#45272