What is the USB-IF and why does certification matter?
The "Universal Serial Bus Implementers Forum" is a non-profit corporation founded by the group of companies that developed the Universal Serial Bus specification." To put it another way, the USB-IF creates the standards that have enabled billions of USB devices and hosts to inter-operate and "just work" over more than the last 20 years.
USB-IF certified products have passed rigorous testing to ensure that they comply with specifications and perform as advertised. Achieving certification requires higher-grade materials and manufacturing processes to ensure the best possible data integrity, performance, and production consistency which may be lacking in cheaper commodity cables.
Standards-compliance is especially important with USB-C cables given the much higher current available per the USB 3.1 spec. Non-compliant cables can potentially cause damage to your devices if the cable does not behave according to USB specifications.