When should we use instances with multiple IP addresses? (70/285 technotes for 2015)

It can be useful to have multiple IP addresses to your instance in VPC to do the following

• Host multiple websites on a single server by using multiple SSL Certificates on a single server and associating each server with a specific ip address.
  
• Operate network appliances, such as firewalls and load balancers that have multiple private ip addresses for each network interface
• Redirect internal traffic to a standby inatance in case your instance fails by re-assigning the secondary private ip address to the standby instance

References:

http://amzn.to/1zq6M7g