What product information is usually missing from advertiser-provided materials?

As an advertiser, we try to provide affiliates with enough information to understand the product and promote it effectively. But sometimes things that seem obvious from the advertiser's side may actually be important details for an affiliate.

So I'm curious: what product information is usually missing from advertiser-provided materials? What do you often have to ask the advertiser or affiliate manager about before launching a campaign?

Would really love to hear about your experience!