how do you know it worked in this specific case though? maybe Salesforce would have done just as well financially and also saved 20 million or something like that without that ad campaign

And maybe it wouldn't have. But since I don't work for SalesForce's marketing dept, there's no way to tell.

No, I find it odd to spend that much cash on a celebrity endorsement when the target consumer audience (businesses) know that the celebrity is not a Sales Force customer:

"What the heck to Matthew McConaughey use SalesForce for ?"

  or more importantly:

"Why is SalesForce paying that kind of money when they could be investing instead in their abysmal support?" - as a SF/Tableau customer this is my perspective.