I like to say that there is no such thing as bad light, there are only bad photographers. That statement is usually true but with a macro lens, it's always true. Whether photographing in bright sun or overcast skies, there are always subjects worth photographing with a macro lens.Macro photography also allows you to break the formula so common in typical wide angle landscapes (strong or leading foreground element, dominant background element, and dramatic or colorful skies), and focus on more abstract features like colors, shapes, patterns, and textures. While the compositions may not be as obvious, to me they are usually more personal and more creative, and they can also help develop your eye for all types of natural photography, including wide angle landscapes, intimates, and abstracts.
One other major benefit of macro photography is that there are subjects everywhere, from your backyard, to flowers and foliage in neighborhood parks or trails and wilderness. You do not need to plan an expensive trip to find worthy macro subjects, and while an area might only yield one good wide angle landscape photograph, it could easily yield a dozen good macros.
For example, I took the following photographs on a single visit to the Denver Botanic Gardens, on a hot summer day without any clouds (usually not good conditions for landscapes but perfect for macros!).