Dual rate and MFU operation

[Supermario]

Hey guys. I am very Radio illiterate...Just learning about radios with dual rate and just need clarification on how it works on a MFU.
From what I've read , by setting the rate of one channel to 100% is that in essence telling the MFU the same thing as if you use manual trim tabs to turn lights on etc? If so, do you set the other rate to 50% for normal operation?
I have as of yet not installed or even removed from box but figured I should get educated now so when it's time to install I won't feel like ripping it out in frustration for not working
Saw a couple instructional videos on YouTube that helped understand how to navigate through the screens and options...
Thanks for any info and insight.

Mario