When this option is set to "high" you will notice an improvement in the quality of many of the graphics in Aeris Calendar including the background image, icons, clock etc. Setting this to "low" will improve performance when the Calendar is drawn. The difference in quality may be subtle in some cases and very noticeable in others -- it depends on the image and your system. You may notice the most difference on the edges of objects, and the most significant differences can be detected when you use a rendered image such as "Bubbles" or "Stars" as opposed to a photograph. Modern systems should set this to "high" without noticing any degradation in performance.