Originally Posted by sneather
To make sure I'm clear, are you talking about normal maps? You said "displacement" but isn't that a third option? Bump / Normal / SPD
My post was related to the one before with the reference to displacement.
Bumpmap and Normalmap don't change the geometry of an object and are therefore only able to affect shading.
A Bumpmap will give you a "virtual" elevation of the surface along the normal of that surface.
A Normalmap is the same but directional so you can create much more detailed features, than the geometry actually has.
Displacement will either modify existing geometry based on the material settings or even create subdivisions at rendertime (SPD). Different to Bump and Normalmapping it allows for correct contours, shadows etc.
Technically they are very similar, you can use a normal or bump map with displacement, or vice versa.
For example sculpted objects most often don't use the fully subdivided geometry but a much lighter one plus a normal map baked from the original highest subdivision level sculpting.