Nozzle size is a whole-print decision, not a per-feature one
Swapping nozzle size changes far more than how fine a detail you can resolve: it changes every wall's line count, every infill pass, and the overall print time for the entire part, not just the section with the smallest feature. Choosing a nozzle based only on the tiniest detail in the model, without weighing the rest of the print's time cost, is a common way to end up with an unnecessarily slow print for a detail that only matters in one small area.
How the comparison works
A nozzle can reliably resolve a feature at roughly one and a half times its own diameter or larger; candidates that clear your stated finest feature are treated as capable. Among those, your time priority picks a specific size: a high time priority favors the largest capable nozzle, a low priority favors the smallest (finest) one, and a medium priority lands in between. An abrasive material adds a hardened-nozzle note regardless of size, since brass wears quickly against filled filaments at any diameter.
Worked example
A 0.8 mm finest feature, medium time priority, non-abrasive material: 0.4 mm and 0.6 mm nozzles both clear the 1.5x threshold, so the tool recommends the 0.6 mm nozzle as the medium-priority middle ground, roughly 1.5x faster per wall pass than 0.4 mm, with 0.4 mm shown as the alternative if finer margin on that feature matters more than the time savings.
A common mistake
A frequent error is swapping the physical nozzle without updating the slicer profile's line width and flow settings to match. A slicer still configured for a 0.4 mm nozzle after a 0.6 mm nozzle is installed will under- or over-extrude across the whole print, producing quality problems that look unrelated to the actual cause. Always update the full profile, not just the nozzle itself.
Limitations
This compares nozzle sizes for feature resolution and relative time, not an exact slicer time estimate. Confirm your slicer profile matches the physical nozzle installed; a mismatch here is a common and avoidable print-quality problem.