Calling footfaults is important
I noticed that a 4.5-ish guy had a nice serve. Then I noticed he used a pinpoint stance. When I started focusing on that, I noticed that he had a complicated footwork pattern and his right foot was smack on the baseline and even perpendicular to it, as he served. Once when he served into the net, he said that he lost his footwork rhythm. That told me that he would have trouble if asked not to footfault.
Then I had a revelation. It is not about whether a few more inches forward makes any difference on the serve. It is really about whether the server can cope with the additional pressure of having a footfault called on him.
The best analogy I can give is say, you are allowed to serve long, but you will be highly appreciated if you serve within the service line. Most players would be very relaxed and actually get their serves in. Then tell them that the rule is now being enforced, and they will start faulting.
Footfaulting is cheating. I have sometimes watched doubles and jokingly threatened that I would act like an umpire and call footfaults. Usually, the serves went south after that, and I had to move on before my "friends" became hostile.
Please ensure that footfaulters are not allowed to get away with what they are doing. Watch their serves breakdown when the rule is enforced and have a good laugh. Watch 4.5s end up with worse serves than a 3.5, and get mighty angry in the process.