Iterations are intermediate steps the Auto-Layout engine generates as it works towards an optimal layout. Initially, there may be significant differences between iterations as the AI refines placement and routing. Over time, these changes become smaller, and the process approaches convergence, where further iterations show no meaningful improvements.

Convergence
Convergence occurs when the layout stabilizes, either due to reaching the best possible arrangement, or when iterations have no meaningful changes between them.

Viewing Iterations
While Auto-Layout is running, you can review iterations using the scroll bar at the bottom of the page:

Drag the scrubber to view available iterations in real time.
If you find a promising layout, click on the check button to apply it to your project to save it permanently.