Most players have a position on the mat they use consistently. When there are bowls in your line short of the jack, moving around the mat can be another part of your arsenal. Your bowl should in theory follow the same arc for the same delivery. Moving your position on the mat can create options.
Top Tip : When bowling on a ditch rink moving to the inside of the mat to tighten your line can give you extra margin to the ditch. Alternatively, on other rinks, moving either way can help you avoid known runs.