The spacenavigator is sufficient for solidworks. It is typically used with your free hand and provides pan/zoom/spin fuctions whilst part selection remains on your mouse, this speeds productivity particularly with assemblies. I would estimate that the improvement is 30-50% over just a std. mouse. Also most of you who like me used the arrow keys to roll the model found that reduced laptop keyboards were a problem so this mouse solves this also. Really if you have already spent $4000 on your SW license it make sense to increase the usability of your investment by spending a little extra on a 3d mouse.