What is the difference between ad hoc distribution and app store distribution in ios

I am new in iPhone development. I have a little idea about app_store distribution. My questions are

1. what is the need for ad hoc distribution in ios application distribution?

2)Is any other license needed for ad hoc distribution from Apple?

if anybody knows, please help me. Thanks in advance.

Ad-Hoc Distribution: Distribution builds of an app, which can be installed on 100 devices designated by the developer on his provisioning portal. The distribution mechanism can be websites, mails or OTA. These type of builds are generally for beta testing or demos.

App-store Distribution: Distribution builds that are intended for general public(for sale). The distribution mechanism is App store only.