This needs further insight, which is why I've assigned it to Wolf for recommendation.
Here's why: Save Test Day and Load Test Day are old, half-implemented controls limited to a single day, and in this layout, are easily confused with Apply Changes to Region: http://screencast.com/t/IlGpXr45Nbol
Save Test Day could be replaced by a feature that allows you to save a whole day containing sky presets, or within current intended functionality, is basically Apply Changes to Region, since it saves the day cycle to the region.
Load Test Day's functionality is approximately replaced by Revert Region to Default, since if you don't save a test day, it just loads the default day cycle.
One good use I can think of for this limited feature is if someone wants to save a day and apply it to another region of their multi-region estate. I can't think of another current way to do this, but I'd like a way such as a dropdown letting you pick a day cycle from the regions you own/manage.