As an Admin / Account owner, you can assign a default cost center to any user.
To do so, go to Settings > Members > Click on the member > Click on "Edit profile" > Cost center.
What is the purpose of a default cost center?
It allows a user who spends most of the time on a single cost center to avoid having to select his cost center each time he makes a purchase request or a payment.
Indeed, the "Cost center" field on a request will be automatically pre-selected. However, if necessary, he can always edit it and select another cost center for a purchase request or a payment.
In the following example, Clément spends 90% of the time on the Marketing cost center, so we have chosen to assign Clément the Marketing cost center. This will be pre-filled by default as soon as Clement makes a request/payment. However, Clément can always select another cost center when making requests and payments if necessary!