This is a policy vigorously enforced by the Co$. The basic idea is that a parishioner intimately connected to a Suppressive_person or SP, someone who holds them back, invalidates them, makes nothing of them, will not do well with Scientology services. Theoretically, this makes sense, at least to a Scientologist. The correct thing to do technically is to make the parishioner less the effect of the suppressive person.
If the parishioner is not able to accomplish this, then as a supposed last resort, the parishioner is to disconnect from the SP, i.e. sever all communication lines.
One longstanding Church policy is that a Church parishioner may not continue to support the SP in any way. If the SP is continually making nothing of the person, it shouldn't be any hardship to disconnect from the SP.
However, this policy goes horribly awry when someone is officially declared to be an SP who does not exhibit the technical characteristics of one, who does not invalidate people, who does not make nothing of one. There are many, many cases of the CofS declaring someone SP who does not agree with the Church's International Management (Int Mgmt) people, perhaps when Int Mgmt have been doing something against policy, when that person is actually helpful to those around him. The result is great upset.