Do I need to connect both the DVI cable and the 15-pin D-Sub cable of an LCD monitor to my desktop?

Recently bought an LCD monitor but got confused by its instruction manual. I am wondering if I need to connect both the cable provided or simply choose between using either the 15-pin D-sub cable or DVI cable.
That solves it. Thank you very much guys
Thanks to all of you guys!! Choosing the best is the hard part but well, its the rule.

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