The red tints along the staves indicate that you’ve done some manual staff adjustment. (Not Frame Breaks.)
It will change the gaps for all systems in that LAYOUT.
In this example, our System gap in Layout Options is set to 4 spaces. Justification is adding an extra 7 spaces.
As long as our gap setting is less than 11 spaces, we won’t see any change to a justified page.
If you have another page that’s got 18 systems on it, then you can use Frame Breaks to force those together, if they exceed the gap settings.
Dorico is all about setting global options that cover the majority of the work, then making a few manual adjustments to fix the edge cases.