This!
"Appeal" might be too big of a word, it's more of a utilitarian thing - but IMO an incredible one. Or, the other way around: the lack of global blocks on the Helix made me go back to a hybrid board.
It might not be relevant for many (maybe even most) people, but for my kind of gigs/jobs, it's absolutely crucial to be both flexible while still being able to adjust my entire setup to accomodate some situations.
And most often it's really simple things. Such as: Clean channel not loud enough generally? Well, with 10+ patches using clean sounds, it's impossible to adjust those during a soundcheck. And even if you managed, what if you overcompensated? You're f*cked. With global blocks it's every bit like a traditional amp setup (controlled by a loopswitcher). Turn your clean channel up once, done. And even if you went too far, no problem, you could even fix this while a chord/note is ringing out.
There's a bunch more of useful "side effects", but the above is the most important thing for me.