@SteveF-M3LR I will get to your question in a second, but first, I have to address this.
As far as I know, the Charge Rate was put into the Appp, because when you use a non-Tesla destination charger you need to be able adjustbthe charge rate seeing that the car cannot talk to a non-Tesla Wall Connector...
No. Tesla can communicate the J1772 signaling language just fine. The J1772 stations signal the maximum amount of amps, and the car understands and sets its maximum for that, and it works perfectly, with no user interaction needed.
OK, now back to our regularly scheduled program.
If the charging rate in amps doesn't matter, why did Tesla put in the ability to change the charging rate in the app?
Two things, why did they put it in the app, specifically? Because a bunch of Tesla owners whined about having to go to the car to change it on the touch screen.
But I think you're asking why is this ability to change the amps even there at all. There can be a few reasons for this, but mainly if people need to do something a bit non-standard. Here are a few examples:
1. Some people want to use energy that is coming in directly from their solar panel generation, and their solar panel system may not be generating at a high enough level to keep 40 or 48A continuous to the car, so they will turn it down to some lower level that the solar will be able to provide.
2. If you are charging at a campground site, sometimes the wiring and outlets in those can be pretty old and crummy or the wire runs really long, so pulling the full amp level trips the breaker frequently or causes the voltage to sag too much. So dialing the amps down some will sometimes enable it to keep charging.
3. If you are having to use some long wiring or extension cords. I have done this one. I was traveling several years ago before the city had a Supercharger or much else public charging infrastructure. So I was running a 30 foot extension cord up their driveway and in the side kitchen door and down the steps to the basement to plug into a dryer outlet. With those extra connections and distance, I didn't want to press my luck running it at the most it could go, so I turned it down a few amps.
4. If you are crossing from one Tesla adapter plug to another third party adapter cord that is for a different number of amps. The Tesla adapter you put into the charging cable has a chip that signals what number of amps it should use. That's all fine if you are using the correct plug type for the outlet. But some years ago, Tesla used to have a very small selection of plug types available. So we had to do some hokey stuff, like using the Tesla 14-50 and then using a little 1 foot cord to adapt it to a 14-30 for a dryer plug. The car can't see that it's only a 30A outlet, since it has the Tesla plug for a 50A outlet, so it can draw too much if you don't manually turn it down.
So that feature of letting people turn the amps down is an important option to have available, but if you are doing very standard things like using the proper plug type or an official charging station, you shouldn't need to adjust that.
