Meshes - Minimize UV seams

Seams are edge cuts inserted into a mesh during UV mapping to help it unfold, flattening out into a 2D space for the purpose of texture assignment. This process is achieved in 3D modeling software, but the cuts it makes are highly important for properly unfolding a model and getting it to look as intended inside Unity. An edge is classified as a seam in UV space when it has only one neighboring face, as opposed to two. Essentially, the seams determine how a mesh's UVs are cut apart into separate UV shells or UV islands, which are arranged into a final UV layout. This layout maps a texture onto the mesh surface, as follows:

Always minimize UV seams where feasible by joining together disparate edges, shells, or islands, forming larger units. This is not something you do in Unity, but in your 3D modeling software. Even so, by doing this, you potentially reduce the vertex count and complexity of your mesh. This leads to improved runtime performance in Unity. This is because Unity must duplicate all vertices along the seams to accommodate the rendering standards for most real-time graphics hardware. Thus, wherever there are seams, there will be a doubling up of vertices, as shown here: