How Important is it to Know the Correct GC Column Length?

All gas flows in a GC system are controlled by the electronic pneumatic control (EPC). The EPC calculates the flow from the applied pressure, nature of the carrier gas, and the column dimensions. Variations in the carrier gas flow rate will result in retention time issues; therefore, it is important to input the correct method conditions into the system. However, how important is it to know the exact length of the column?