On pushy water, flouro doesn't resist sinking through the water column as much, as mono.
The sooner the fly gets down the better.
Every little bit helps, when it comes to opening the fishes window for shopping time.
Droppers when nymphing, are my big uses of this expensive stuff.
I use about (3) 100yd spools of 4X, 5X, 6X respectively, in a season. 8-10 inches at a time.
"Life's too short to fish poorly".