From Fedora Project Wiki

The following needs to be updated for the SCL Guidelines:

Software Collection Macros

Software Collections are to be kept to separate packages from mainstream packages similar to how MingW packages are managed.

In the past, SCL macros were allowed to be present inside of mainstream packages if they were not used. Since we're now building SCLs, we are now enforcing a strict separation. Packages MUST be updated to restrict SCL macros to only those packages particularly approved as part of an SCL.