[Blender]UV welding tools. stacking UV

[Lonecat Nekophrodite]

New unit. new challenge to make a uv map before applying textures. what's the use of UV welding? when stacking identical UV islands (including mirrored ones) will 'weld' command cancels UV and thus the stacked UV will not recieve the same texture paints or will it accepts the same paint? and will paint or texture distributed evenly to every pieces stacked in the same island??