It is not likely due to meteorological conditions affecting the physics of the radio waves (as others have mentioned the difference between the top and bottom of the aviation band is not very large, and ATC has no easy way of tuning a frequency on the radio).
In the center environment I am not sure why a certain area would be on one frequency one day and another frequency on another day, unless both the main and backup equipment for the usual frequency was inoperative and they were using an entirely separate standby frequency. Some sectors will have these and some might not. Center sectors are very static, and even if two or more sectors are combined controllers will generally have you use the "proper" frequency for your area. This will ensure proper radio reception and make things easier if the sectors need to be decombined.
In the terminal environment, however, which airspace is owned by which controller (departure, initial approach, final approach, etc) can be highly variable depending on runway configuration. At a smaller Class D or class C there might only be one frequency for the entire TRACON, or an east/west or north/south split that doesn't change. But at a Class B TRACON the controller overlying your tiny airport in the morning might be different from the controller overlying it in the evening.