Network Address Translation

Purpose of NAT is to hide the internal IP. Purpose of using NAT Was to save the IPv4 Range. IPv4 is 32 bit.

Private IP Range 
Class A-  10.x.x.x
Class B- 172.16.x.x - 172.31.x.x
Class C- 192.168.x.x

It also provides privacy as it conceals identity. Remember GDPR considers IP Address is PII.