These Import Options display when you select 
> Import Layer in the Sculpt Layers window.
- Match By
-
Indicates how the imported model corresponds to the active object. Select from the following options:
- Vertex IDs
-
Indicates that the imported model is topologically identical to the active object.
- UV Positions
-
Indicates that the imported model does not have an exact Vertex ID correspondence to the active object. Use this option, for example, if there have been updates to the imported mesh that change the model's topology, or in any situation that doesn't allow for an exact correspondence.
- Delta to Base Layer
-
When on, imports the model to a layer, ignoring all layers except the base mesh (default). When off, all layers including the base mesh are considered during import.