The decision to anticipate Yukina's Rescue Arc
They decided to bring forward Yukina's arc to provide a sympathetic backstory for Hiei, who, in the original work, was still an antagonist until being pardoned and joining the heroes in the "Four Beasts" arc.The fate of the "Dark Tournament" Arc
Considering that the original manga/anime has three Tournament Arc (Genkai's Successor, Dark Tournament and Three Kings), it is possible they decided to keep Toguro and delay the other elements of the arc for a possible second season, in order to avoid being repetitive.