GaussView’s point-group symmetry feature allows you to increase the symmetry of the current molecule. A molecule can be constrained to a specific point group, and all future modifications to the structure will maintain that symmetry.
GaussView 6 now allows you to reduce the symmetry of a molecule you are working on. Preserving some molecular symmetry is useful for setting up calculations that involve Jahn-Teller distortions. The graphic below shows the current point group being modified from D3h to D3.