Questions about OSPF lab

Hi

I have consulted Narbik's OSPF labs

I don't understand a case concerning OSPF redistribution between NSSA and area 0.

For this lab this command is necessary :

area 1 nssa translate type7 suppress-fa 

I have made a ton of redistribution between NSSA and the rest of the world without using this.

If you have the narbik lab for cccie rs v4.0 it's lab 19 in OSPF part.

I suppose that the FA suppression on the router should be the reason but I don't see precisely why.

Thanks for help.