The Sigma USB dock makes it possible to connect the C, A, and S lenses to your computer, in order to use the Sigma Optimization Pro software. This way, you'll not only be able to update the lens's firmware, it's also possible to adjust the lens's focus parameters.
Several focus settings are available to fine-tune the parameters in the lens until they're exactly according to your preference. This'll provide you with an important service. Instead of having to send the lens away, you'll have 16 categories at your disposal to adjust the lens focus (4 options for the focal length x 4 options for the photography distance). For Sigma's sports line, there are also 3 AF speed modes you can fine-tune, 3 optical stabilization modes you can adjust to your liking, and you'll have the option of adjusting the focal distance adjustment.