ForgeFlower is better than Spigots FernFlower at decompiling the source.
However, in order to maintain the CraftBukkit patches, we must keep
using spigots for the primary.
However, for any file that we import on top of Spigots imported files
there is nothing stopping us from using better decompiled files.
So these changes will use ForgeFlower to maintain a better set of
decomped files, so anything we add on top of Paper can start off
in a better spot.
Aikar
Zach Brown
Byteflux