Yes. You do not want to put the plant into a dry hole, as planting into a dry hole will damage the roots hurting your yield or dry out your clone which ever the case may be. With Rockwool the pH is high, so you need to presoak it to lower the pH. Having the pH too high cause nutrient deficiencies & toxicity and can also damage the roots causing root rot and disease problems. With some mediums and soil, you presoak to get out clumps that cause dry spots. If you have a clump of soil or medium that is not wet and the roots grow into it they will die back. If the roots die back back they start to rot which hurts your yield.