Overhangs and bridges fail for related but different reasons
An overhang sags because each new layer has less material below it to bond to as the angle increases; a bridge sags because the extruded line has to span open air with nothing beneath it at all until it reaches the far side. Both depend heavily on how well a material cools, which is why a material that handles a 50-degree overhang fine (PLA, with strong part cooling) may not handle the same overhang if the same geometry is printed in a poorly-cooling material like ABS/ASA. This scan checks both features against a cooling profile you choose, not one blanket assumption.
How the scan works
Each cooling profile carries its own general overhang-angle and bridge-span planning limits, tighter for poorly-cooling materials, looser for well-cooling ones. Your entered angle and span are compared against those limits, and either or both can be flagged independently, since a part can have a fine overhang but a risky bridge, or the reverse.
Worked example
A 50-degree overhang with a 30 mm bridge span, PLA-like cooling: the overhang clears the roughly 55-degree limit for this profile, but the 30 mm bridge exceeds the roughly 40 mm limit only slightly, and if you instead select poor cooling (ABS/ASA-like), both the overhang and the bridge span move into concern, since that profile's limits are considerably tighter.
A common mistake
A frequent error is scanning a part's overhangs and bridges once at the design stage and then never re-checking after a slicer or settings change. A cooling profile that comfortably handled a given angle before a firmware or fan upgrade may handle it differently afterward, in either direction. Treat this as a check to repeat after a meaningful hardware or profile change, not a one-time approval.
Limitations
These are editable, printer- and material-dependent planning limits, not universal thresholds. Your printer's actual cooling hardware, print speed, and slicer settings all shift these numbers in practice; treat a flagged concern as a signal to check the slicer preview or test a small sample, not a guaranteed failure.