UV Tools

These tools essentially provide those functions which allow you to mark seams for the “Unwrapping” process:

Add Clusters: Use LMB to mark the cluster (UV Islands) center on faces. Click the cluster again to delete it.
Like the geometry they represent, UV points can be connected to form a larger shape referred to as a UV shell in Maya, a UV island in Softimage, and a UV cluster in 3ds Max.
Despite their different names in different applications, they serve a common purpose. Often when working with these shells, some of them may overlap in the UV editor. If this happens, the texture will appear to repeat. Unless there is a specific need for it, as there sometimes is with game textures, overlapping UV shells should generally be avoided.
Mark seams: Let’s mark a discontiguous set of connected edges. Mark seams on the UV-Map. CTRL+LMB unmarks a seam.
Edge loops: Select and marks contiguous edge loops on your topology. Mark entire edge loops on the UV-Map. Use CTRL+LMB to unmark them.

The option “Extended edge loops” in the edge tools tool (uv/retopo), useful if you have “approximate” edgeloops and need to mark seams. Super useful for making seams over triangular mesh.

UV Path: Allows the selection of vertices interpreted by 3DCoat to provide the path for a connected series of edges. Put a path along the shortest path (under certain criteria) between several points. Click to add points or split lines, use RMB, or double-click to remove points. Press ENTER to mark seams, and CTRL ENTER to delete seams. Use different criteria to adjust path flow.
Join Clusters: Hover the seam between the clusters and click to remove the whole seam and join clusters.
If the highlighted seams are red, the resulting summary islands have self-intersections or too big square trash. If it is green, the summary island has no self-intersections, and square trash is no more than 1/2.

Tutorial

Retopo Room Pt.3: UV Edit: This video touches on some of the UV tools in the Retopo Room during this walk-through.