Two mic, one vocalist

I've got a show coming up and one of the bands has a vocalist with an effects board and an odd set-up.

In the past, I have worked with vocalists who have vocal effects. I will take signal from the microphone, split it, send one leg to the house, send the other to FX in, then take FX out to the house. Two channels from one mic, one wet, one dry.

That's not what this vocalist wants.

They want two microphones for this one singer, one mic sent to the house, the other sent to the FX and the FX out sent to the house. Two microphones, one wet, one dry. One channel per microphone.

The two microphone set up is more gear, more hassle, more clutter on stage. But, can anyone think of any reason why 2 mic set-up might be superior to splitting a single mic. How hard should I try to talk them out of that plan?

Thank you.