Vertex Painter lets you easily create weight paint (vertex grups) and vertex paint under four different functions with a few clicks. The functions are called "Island", "Camera", "Slope" and "Altitude", which are described in detail further down, can be combined into one. Vertex Painter also sets up nodes in your active material already assigned to your vertex paint to for example combine different materials easy and quick. All of this features can be made manually as well but can be uninspiring and shift focus on being creative and getting your visions realized when using Blender.
Island mode lets you create vertex and/or weight paint on an object where two objects overlap. For example, it can paint out a shoreline where a clif meets water and thereby use the vertex paint in your material node setup (attribute nodes) as a mask where the water foam should be for a smoother transition. You can then flip the function to create a darker cliff edge closer to the water. It can also be used around a house to create a path material and then the rest of the plane as grass. Weight paint can also be used in island mode which for example can let you grass grow around a cliff edge to yet again smooth out a transition between objects. The falloff/decay of the paint from an object is easily determined by the settings.
Camera mode is what it sounds like, creating paint only within your active camera. This allows you to reduce the amount of unneccessary CPU power while working in your project and only have the for example paricles in weight paint mode where the are seen. Camera mode, like island mode, also has a decay feature so you can for example have increasing (or decreasing) amount of weight in your camera view.
Slope mode creates paint determined on the slope of the mesh. For example, you seldom want to have trees growing on a cliff edge but ususually where it is plain ground. Or perhaps to have a rock material where the slope angle is highest and grass, sand etc. where it is more plain. The settings allow to set the slope thresholds exactly as you like with a few clicks, also with the opportunity to invert the paint.
In altitude mode, you can set the paint depending on the height or use it as a gradient in any of the three axis. It allows you to for example only grow grass/trees above the waterline in weight paint mode, or perhaps be used to have snow on the top of mountains.as a mask in vertex paint mode.