Adaptive layers help some parts a lot and others not at all
Adaptive (variable) layer height automatically prints finer layers where a surface slopes or curves, where visible stepping is most obvious, and coarser layers on flat or vertical sections, where it is not. That makes it genuinely valuable for a part dominated by curves and organic shapes, and nearly pointless for a part that is mostly straight vertical walls, where there is little sloped surface for the feature to optimize in the first place.
How the decision works
The tool checks whether your part actually has meaningful sloped or curved geometry and whether it is instead dominated by vertical walls, which would blunt adaptive layers' benefit regardless of other features. If sloped geometry is present and time minimization is not the overriding goal, adaptive layers are recommended; if time minimization is the priority, a simpler fixed coarse layer height is recommended instead, accepting more visible stepping on the curves in exchange for the fastest print.
Worked example
A part with meaningful curved features, not dominated by vertical walls, balanced time goal: the tool recommends enabling adaptive layers, since the geometry has real curved surface to benefit from it and the time goal does not override that benefit, with a fixed fine layer height shown as the alternative if adaptive layers behave unpredictably in your specific slicer.
A common mistake
Makers sometimes enable adaptive layers as a blanket "always on" setting rather than a per-part decision, assuming it can only help. On a part that is mostly vertical walls with little sloped geometry, adaptive layers add slicing overhead and unpredictable time estimates for essentially no visible benefit. Treat it as a tool for the right geometry, not a default to leave on for everything.
Limitations
This compares adaptive and fixed layers qualitatively based on your described geometry and time goal; it does not simulate your specific slicer's adaptive-layer algorithm or predict an exact time savings.