AWS Placement groups

Question

According to the AWS,  AWS placement group is needed to be able to utilize 10gbps network utilization and performance.
With that instances are required to be placed in same availability zone for placement group, this sounds risky. For ex, unavailability of one availability zone would bring down the infrastructure. Considering the risk, why would you use placement group?

Answer 1

Placements groups, as the documentation states, is for those applications where it requires the fastest possible network speeds between your instances, and because of that the instances can't span/increase availability zones.

However, just because you have some of your machines in a placement group doesn't mean you can't also have a duplicate set of machines in another placement group in a separate AZ or even a separate region for your DR / redundancy needs