There is a large difference between how this is supposed to work in theory , and how it works in practise.
Suppressive person is a technical term. It describes someone who used to be called a Merchant of Chaos. Such a person is mentally stuck in a long-ago incident, and so does not perceive what non-SPs see at present time. The SP identifies everyone around him with his enemies in that long-ago time.
One of the policies of the CofS is that the Scientologists they hold sway over, the churchies, must disconnect from people the CofS declares to be SP. There is a technical reason for this, namely that preclears intimately connected to such persons don't hold onto gains they make in auditing, as they get continually restimulated by the SP.
This all makes sense, as long as the SP Declares are accurate. When SP Declares are done based on whim, or because the person concerned pointed out some out-tech or off-policy action done by Int Mgmt, that is a different story. In such a case, a churchie can be made to disconnect from a loved-one for no good reason, and upset will often ensue.