Yeah, if you are growing in soil, and/or using organic nutrients then you will need to ffeed the microbes in the soil to get them going, and to help them multiply so that they can process the organic nutrients. If you are not using organics/"natural" soil then you don't need to use the molasses. I think most who use it put about 2-3Tbsp into a gallon of water.
I am currently running all organics and used molasses for the very first time this run. I used one tablespoon per gallon of water given every three weeks. Although I didn't run a control to see if it has any actual growth results the girls seem super healthy. It is really cheap so I believe I will continue it's use.