They don't.
"At low engine speeds a single throttle body opens for efficiency, with the second throttle body opening in synch at higher engine speeds to maximise power."
ford performance is the same warranty on the F150 kits, they just add their logo to the whipple warranty paperwork, so I assume it's the same on the Mustang
https://www.f150forum.com/attachments/f123/578875d1705119589-new-23-v8-whipple_frpp_wrnty_r6_8_17_22.pdf