To create a Binary structure, yes, you do need to enable the Forced Matrix. This will allow you to limit the Width of your structure to 2 (Set the Width to 2). Now, you do need to set a Depth. This is a safety feature to prevent you from generating more in commissions than you make on each sale.
The Depth controls the number of Levels you have in your structure so, if you leave Depth empty, you won’t be able to have any Sub Affiliates.
If you set the Depth to a higher number than the number of Levels you setup in the Per-Level Rates, it uses the Global Indirect Referral Rate and Rate Type.