I tend to see deism brought up in three circumstances:
- The person lacks modern understanding of things, and some god is a good placeholder for unanswered questions. See: the founding fathers.
- The person is non-religious, but isn't quite ready to give up on theism all together. The god they are left with is extremely vague, because they don't want to make claims that can't hold up to scrutiny.
- The person is actually a non-deistic theist, but for the sake of the argument at hand, they don't want to commit to anything more specific. See: Intelligent Design proponents. Most of them believe that Jesus died on a cross for our sins, but they realize that's a harder sell than trying to invoke the Cosmological Argument.