Dynamic Defaults for Custom Segments
When you use dynamic defaults, you essentially create a relationship between multiple record types that use a segment. If you try to create this relationship before you've applied the segment to all of the applicable record types, the system displays a message regarding record application. This message states that the system will apply the segment to the record type referenced in the Source List choice that you've made. You can cancel the change, or you can let the system apply the segment to the additional record types.
For more information about sourcing, see Dynamic Default Value Sourcing for Custom Segments.