Are there some common use cases that were anticipated when deciding to support assets that require authorization in order to set up a trust line?
As I understand it, the main use case is to support KYC (know your customer) and anti-money laundering. An issuer can confirm identity in order to satisfy relevant laws in their jurisdiction, and then proceed to grant authorization through an allow trust operation.
You could also use this mechanism to limit a set of tokens to some pool of people for other reasons. For example, if you wanted to create a neighbourhood currency to "keep spending local", you could create a token that can only be traded within a certain city (and require proof of address before you allow distribution). Or you could allow tokens to be held only by members of a particular club, society or promotion (e.g. like air miles or "non-transferable" coupons or points).
Limiting access could also protect you from the wider free market and allows you to control exclusivity. Perhaps you just don't want your token arbitraged by professional financial people.