What is the mental factor of Adhimokkkha (determination) use for?
In the Mahasi tradition (and perhaps others), resolutions are used when training the mind so that a certain type of insight (vipassana stage) arises during the practice -- most often the supramundane stage (cessation/fruition, magga-phala-nana), but also the lower stages (from A&amp;P up to equanimity). The object of the resolution is stated in the mind (or aloud) before the practice, then let go. See Mahasi's great Practical Insight Meditation for details on that.