Using “varchar” as the primary key? bad idea? or ok?

Question

Is it really that bad to use \"varchar\" as the primary key?

(will be storing user documents, and yes it can exceed 2+ billion documents)

Answer 1

I think int or bigint is often better.

1. int can be compared with less CPU instructions (join querys...)
2. int sequence is ordered by default -> balanced index tree -> no reorganisation if you use an PK as clustered index
3. index need potentially less space