Visual filters enhance the contrast of certain features or objects by blocking either light of the same color as that feature, or light of the same color as the feature's surroundings. Most visual filters are relatively clear in the near-IR, limiting their value for CCD observing.
Wratten #38A filters are said to boost the contrast of Jupiter's belts and Great Red Spot, and may make it slightly easier to see comets' gas tails.
Our filter's coatings are slightly damaged around the edges. However, since the light beam inside the telescope will only pass through the center of the filter, this should not affect performance.