This is a more technical description of what a dual processor (utilizing multi-threading) can do in SolidWorks. Documents are retrieved in multi-threaded mode. When you retrieve a (large) part/drawing/assembly, the document will immediately display the document in a View-Only state while the actual document with all components and features is being retrieved in the background. During the View-Only state, you can use all functions supported in the SolidWorks Viewer (Zooming, Rotation etc.) but you will not be able to switch to another document or start opening another document. After the retrieval of all necessary models is completed, SolidWorks will automatically switch to the normal edit state.
There are low level operations in SolidWorks modeling algorithms which use multi-threading (e.g. Boolean, silhouettes, line generations, mass properties, body check). These operations become multi-threaded in SolidWorks operations like a cut-extrude or a boss. However, SolidWorks doesn't use the low-level modeling algorithms on a one-to-one basis, therefore the overall effect may be hard to determine based on the configuration of the body and the complexity of the topologies. The most obvious area of improvement the user can see is in mass properties and in body checking because those operations directly use the low level modeling algorithms. In general, the solving process used for parametric modeling is, by nature, very linear and cannot take full advantage of parallel processors.
Please note that SolidWorks does not do any specific benchmarking to determine speed gains in SolidWorks from a second processor. Certain operations will benefit from a multithreaded environment, but SolidWorks cannot provide any statistical information on such benefits at this time.