Priming your filters before use is important so as to get out some of the fine particles left behind in the manufacturing process. But sometimes when using the included rubber faucet gasket and priming the filters with your sink faucet, you can get wet or spray water all over the kitchen if you have too much water pressure when priming! (My own personal experience!)
....But the Black Berkey Primer eliminates this hassle and makes thing go very smooth and easy and it gets the job done with the least amount of effort....Also if you are out in the wilderness with the Berkey Go Kit, it is absolutely essential you include Black Berkey Primer in your camping gear or Bug-out Bag Kit since you will not have access to an actual pressurizes water faucet!
Very Cool!