A common pitfall is trivialising the role of design within a company. A designer fills the void between the marketing and the physical creation of the product. A space that is hard to define, but the designer can define for it you. That is why you need him/her and will make up an integral part of your team.
Trivialising the importance of design is one of the biggest and most common mistakes a every company makes. Notions like "how pretty it looks does not ultimately sell the product" are used to justify these, in my opinion, poor business descisions.
More than often these decision however stem from a lack of understanding in what way the design feeds into the end-product. Since this is more about doing proper business analysis I will not dive deeper into this (other, more qualified, people have written good articles this subject). In escense it just boils down to having a good understanding what is important for a optimal flow of business and why it is such a good flow. Knowledge is power after all.