It is always a good idea to help the weakest point of any installation (corners) by adding a small amount of thinset in case you missed something in your back buttering or general installation techniques.  The best floors have full thinset coverage and the corners are the easiest to miss when trying to achieve this goal.  Because of our specific corner design that allows mortar in the corners of the tile to have direct contact with the floor, we have helped you to achieve this.  We would not discourage you from creating small dots of thinset in your corners if if gets you closer to your goal of full coverage.  However, it has nothing to do with the Leveling Spacers system in particular.  It is just a professional’s installation preference on how to acheve proper coverage.  All tile installers have their preferences, and many like to put small dots of thinset in the corners before setting the tile in place.