What is the need of “Custom Controller” in Visualforce as everything can be done by the combination of Standard Controller + Extension class in salesforce?

Hi

1)      Sharing setting is applied on standard object or extension by default, In case we don’t want to apply sharing setting in our code then Custom controller is only option.

2)      A custom controller is an Apex class that implements all of the logic for a page without leveraging a standard controller. Use custom controllers when you want your Visualforce page to run entirely in system mode, which does not enforce the permissions and field-level security of the current user.

Thanks