private IP address

Question

why private IP address is needed?

Answer 1

Consider ISRO. They do not want their lab systems to have public IP as then Internet hackers can try hacking to it. So, they keep all systems private with private IP so that individual systems can interact with each other inside ISRO but no outside system can connect to any. When any system connect to Internet it will be through a router and we assume router is good enough to handle any attacks.