I made a tool to combine skinned meshes together. Here you can see the performance impact using uncombined meshes can have, and with no visual difference between the two, it's literally free
Combining meshes in game without loosing boneWeights - Unity Answers
Dynamic Mesh Combining in Unity with C# - Combine meshes with different colors | Habrador
Dynamic Mesh Combining in Unity with C# | Habrador
10 Common Unity Mistakes | Toptal®
unity3d - Combine meshes in Unity at runtime - Stack Overflow
Editing 3D Meshes in Unity3D | DUST SCRATCH GAMES
unity - Combined Mesh and Lightmap - Game Development Stack Exchange
Creating in Unity #5: Combining Meshes! - YouTube
I have learned that combining meshes into one + having 1 material will drastically reduce the draw calls, this technique is nice, especially on mobile devices! : r/Unity3D
Merge Faces | Package Manager UI website
unity3d - Unity: cannot combine mesh that does not allow access: Cube - Stack Overflow