The purpose of this feature is to make you aware when widgets are
rebuilding—you might not realize that this is happening when just
looking at the code. If widgets are rebuilding that you didn’t expect,
it’s probably a sign that you should refactor your code by splitting
up large build methods into multiple widgets.

This tool can help you debug at least four common performance issues:

The whole screen (or large pieces of it) are built by a single
StatefulWidget, causing unnecessary UI building. Split up the
UI into smaller widgets with smaller build() functions.

Offscreen widgets are being rebuilt. This can happen, for example,
when a ListView is nested in a tall Column that extends offscreen.
Or when the RepaintBoundary is not set for a list that extends
offscreen, causing the whole list to be redrawn.

The build() function for an AnimatedBuilder draws a subtree that
does not need to be animated, causing unnecessary rebuilds of static
objects.