I see people extending late veg and flower. Is there any circumstance you would extend transition phase?
No, transition is technically flower stage but grobo uses it to get the plant ready for flower, not necessary to extend for any reason!
The two stages that extending makes a difference is still gonna be just late veg and flower stages.
Late veg is extended for height gain and repair and flower is extended to bulk up buds and reach desired trichomes.
What @Bplatinum9 said.