Multiple private network adapters can be defined either during the installation phase or afterward using the oifcfg.Grid Infrastructure can activate a maximum of four private network adapters at a time. With HAIP, by default, interconnect traffic will be load balanced across all active interconnect interfaces, and corresponding HAIP address will be failed over transparently to other adapters if one fails or becomes non-communicative.
it is quite helpful in following scenarios
1) if one private network adapterrs fails, virtual private IP on that adapter would be relocated to healthy adapter.
There is very good document on Metalink ( Doc ID - 1210883.1)