“Is to make the support department obsolete, likewise the purpose of marketing is to make the sales department obsolete.”
The perfect product requires no support whatsoever. It installs and performs flawlessly, people who call support will not be worthwhile supporting, so the entire department can be replaced by an automated response system explaining the client how to get a refund.
Similarly, if the marketing department creates “the perfect campaign”, the sales dept. can be replaced by an online shop – no need for the sales people to elaborate on the wonderful features – people already “get it” and just want to know how to place an order.
These are the goals.
In between, there will be situations where support will perform clarification on features because some parts of the application are not well documented, or there are rare fringe situations that require a little tweaking and troubleshooting. In terms of marketing, the sales people will be met by people who “get it” but need justification to make the actual purchase. The same way we fall in love with a car, but need a salesperson to confirm our (sometimes made-up, irrational) justification.