There are three main ways to distribute iOS applications. Each has its own set of advantages and disadvantages.
App Store
The mainstream way of distributing applications. People find, purchase, and download your app directly from the App Store, an application that is preinstalled on their device by Apple.
This method of distribution make sense if you want to make an app available to the general public for either profit or marketing reasons.
Advantages:
- everyone has access
- payment channel is already created
- easy channel for posting updates
Disadvantages:
- everyone has access
- Apple gets a 30% cut of sales
- requires approval process
- possible delays in posting updates
Enterprise
The way of distributing an app to many devices without making it public. Accessible to companies that qualify.
This method of distribution makes sense if you want to make an app available only to people in your company. This method is commonly used by marketing departments that want to create apps for their distributed sales teams.
Advantages:
- non-public distribution
- can distribute to many devices
Disadvantages:
- Apple intends for the distribution to be only within your company
- only certain companies qualify (see http://developer.apple.com/programs/ios/enterprise/ for details)
- need to create a distribution channel (website, email, etc.)
- costs $299 per year
- distribution certificate expires after 1 year
Ad Hoc
The way of distributing an app to a limited amount of devices without making it public. Accessible to everyone with a developer account.
This method of distribution makes sense during development when a limited number of stakeholders are reviewing the application. It also makes sense for limited, one-time use apps.
Advantages:
- non-public distribution
- only requires a developer account
Disadvantages:
- limited to 100 devices
- requires all device UUIDs for app build
- need to create a distribution channel (website, email, etc.)
- apps expire after 90 days