When you choose the "Associate with Existing Gradebook Entry" radio button, you will have the opportunity to select any existing gradebook column from a drop-down list. If no Gradebook columns have been created, the radio button will be absent. Note that it is possible to associate multiple assignments with a single gradebook column.
Points awarded to assignments that have been associated with a Gradebook column will be added to any existing points in that column, up to the maximum points that were allotted for the column. Any additional points will be discarded. Care must be taken not to associate a single Assignment with a Gradebook entry with a lower point value. Under such circumstances, all points awarded for the Assignment can be lost.
One advantage of creating associated assignments is that grades can be adjusted from the gradebook interface, as well as through a gradebook update. This advantage should be balanced against the possibility of instructor error, which can easily result in an inaccurate student grade.