Prevent boil overs on the hot side, add 2 drops per gallon for a nice rolling boil, no worries.
On the cold side, fermcap keeps the krausen in your fermenter to 1/2". in a 6 gallon carboy there is no need for blow off tubing when you use this product. Use only two drops per gallon at the start of fermentation.
If you add fermcap during the boil you do not need to add it again in your fermenter.