Use when porting any widget, dialog, panel, transform, or helper from PlotJuggler 3 into PJ4, when asked to add a UI element or feature that PJ3 already has, or when tempted to write a new one from scratch.
Use for ANY PJ4 performance question on Linux — sluggish plot zooming, dropped frames, GUI jank, a file-load or startup that "got slower", a suspected perf regression from a commit, "why is this slow" — before running `perf record`/`perf report` on…
Use when a PJ4 change is believed complete and it's time to prepare a commit or PR, when tests are red at finishing time and you must decide whether the failure is yours, or before any "done / ready to merge" claim.
Use when confirming a PJ4 change actually works in the running app — visual, widget, layout, or performance changes; before claiming anything is fixed or verified; or when an edit appears to have had no effect after rebuilding.