Traditionally and correctly considered ideal evergreen ground cover for shade, dry or not. The periwinkles are also prolific flowering plants in the spring, especially the V. minor forms. The caveat is that they can spread over time and become difficult to eradicate once they are in amongst other plants. We find a trim over not too long after flowering helps keep them neat and tidy and allows the flowers to be seen the following spring. Don't be too timid, just shear them down to the ground, growth will soon reappear.
The hardy Vinca species provide a welcome splash of colour in shady areas, some from mid-winter onwards; these are welcome to us but also to those bumblebees and solitary bees that emerge early in the season. The dense cover they make is of value as refuge for amphibians and beneficial insects, but equally of concern if and when they spread out of gardens into natural habitats. While that particular cat may be out of the bag in many areas, it would be prudent to try and ensure that plants in the garden stay there.