AS number assignment criteria

Just a quick one about assigning AS numbers.

The reasons for ASN requests we get can be categorised as follows:

1 - "Because the router manual says we need one." 
Needs no further explanation, does it?

2 - "To identify routing processes for internal routing."
Some isolated networks run multiple IGPs and seek unique numbers
to identify them.

3 - "To identify single-homed ASes."
They connect to a service provider or to another enterprise and
use external routing. The other end tells them they need an ASN.
Strictly speaking they do not need one, because they can only have
one external policy.

4 - "To identify multi-homed ASes."
These really need one because they have a unique external policy.

So far we have never assigned ASNs to categories 1 and 2. I see no reason
why we should either.

We have assigned ASNs to some in category 3 because their service provider
required it for their management purposes.

We have always assigned ASNs to category 4.

The question now is: Should we assign ASNs to those in category 3 
who request it because their ISP requires it?
This is a potentially large number.

Opinions?

Daniel