MAF rescaling, cam change

So just curious, if you change the cam, but not the MAF housing etc, do I still have to rescale the MAF and SD errors? Or do I just make changes in the VE tables to get the fuel trims to get closer to 0 than having say, -15 on stft? Which I’m assuming -15 on a fuel trim is that it’s taking out 15% of fuel?

I have made the decision to get very serious serious about learning everything that I can but for some reason I pick up tuning standalones better than these reflashing softwares like HP tuners. So that being said, let me ask you this. Still being new and slowly creeping up with real world tuning experience, how can I learn the softwares so that I know exactly what to do? I was looking in the Holley stand-alone software I will be using in my car and there’s places for offsets and I’m thinking, what in the world is this how do I know what to set these to and how do I use them etc. I want to learn more I need to learn more. Let me know any information.

Signed,

a person becoming/learning to be a serious and knowledgeable tuner