question: `SPAM_SUBJECT` what do the docs mean by "reducing the value of a subject prefix"?

### Subject

Something else that requires developers attention

### Description

Hello,

The description of the new `SPAM_SUBJECT` variable says:

> NOTE: By default spam is delivered to a junk folder, reducing the value of a subject prefix for spam.

Can someone please clarify what does "reducing the value of a subject prefix" mean?

Thank you!