UV layout is an important part of texturing your model. UV mapping operations automatically fit UVs within the default 0 to 1 UV texture space, but working with one texture map can make it difficult to equally distribute detail to every area of your model. You can work with UV tiles outside of the default texture space, applying a different texture to each tile, to maximize the texture's resolution.
You can also work with multi-tiled UV textures that have been created in other applications, including Mudbox, ZBrush, and Mari. When you load multi-tiled UV textures, the UV Editor automatically detects the number of tiles and uses the original grid tile layout. Each tile is labeled with the name of its corresponding texture file. See Loading multi-tiled UV textures through a single texture node.