Avoid processing an already cut-out image repeatedly when the missing information is only available in the original photograph.
Every pass sees a different input
The first pass uses the original scene to estimate the subject. A second pass sees the modified image, with transparent or flattened areas where the scene used to be. It does not have access to discarded details from the first operation. Repetition can further simplify thin parts or weaken soft edges rather than improve them.
Return to the source for changes
If a strap disappeared, reopen the original or choose a better source photograph. If the problem is a halo, inspect the edge colors and consider manual refinement. These are different problems and should not both be treated with another automatic pass. Keep a transparent master from the best result so later layout experiments do not require additional removal.
Imagine a portrait that lost fine hair on its first pass. Running that PNG again cannot recreate the missing strands from nowhere. It may instead make the remaining hairline more compact and artificial.
Judge against a concrete requirement
Decide what needs improvement: an interior hole, a missing part, a retained patch or color contamination. Compare the original and output at the intended display size. Change the input or editing method to address that defect. Do not assume that more processing equals higher quality. A single acceptable pass followed by deliberate manual work can be more reliable than a chain of automatic transformations with no reference to the source.