Yes, ordering of dimensions is very important. The report will be generated based on the order of selected dimensions. Suppose, you want to generate a report of region wise cost for each of the Linked Account. You can select dimensions in 2 different ways.
Case 1: Dimension 1: Region
Dimension 2: Linked Account
This will generate a report with Region as first column and Linked account number as second column. This way, you will be able to get linked account cost, based on all the regions.
Case2: Dimension 1: Linked Account
Dimension 2: Region
This will generate a report with Linked Account as first column and Region as second column. This is the correct way to generate a custom report of having region wise cost of each linked account.
So, based on the view you want to create in the custom report, you need to order the dimensions.