Docking is not a prerequisite but a temporal constraint for fusion of secretory granules.
Kasai K, Fujita T, Gomi H, Izumi T, Traffic, 2008 Jul - link

Secretory vesicle docking to the plasma membrane: molecular mechanism and functional significance.
Izumi T, Kasai K, Gomi H, Diabetes Obes Metab, 2007 Nov - link

Rab27a mediates the tight docking of insulin granules onto the plasma membrane during glucose stimulation.
Kasai K, Ohara-Imaizumi M, Takahashi N, Mizutani S, Zhao S, Kikuta T, Kasai H, Nagamatsu S, Gomi H, Izumi T, J Clin Invest, 2005 Feb - link