Difference between C and en_US.UTF-8 Collate & CType in Postgres 10.x

Hi

Can someone let me know what is the difference we are expected to observe
if we set Collate & Ctype to C as against en_US.UTF-8 with encoding set to
UTF8 in both the cases ?

Name | Owner | Encoding | Collate | Ctype | Access privileges

-----------+----------+----------+---------+-------+-----------------------

postgres | postgres | UTF8 | C | C |

Name | Owner | Encoding | Collate | Ctype | Access
privileges

-----------+----------+----------+-------------+-------------+-----------------------

postgres | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |