Succorers of Imam Mahdi

According to one of Imam Ali’s (pbuh) narrative, “Succorers of Imam Mahdi (hgr) will congregate like autumn clouds. [1]
Do you know the reason of this parable?!

This parable shows tree point leastwise:
1- Acceleration of congregating and its beneficial effect [like autumn clouds which are agile]
2- Being resourceful and not buncombe [like autumn clouds that are pluvial]