The controls are intuitive and there is a pre-selection highlight to help you never miss a cut. The interaction was designed for artists, by artists, to be as fast as possible. 

Left Click: Mark edge as seam

Double Click: Mark loop as seam, stopping at other seams (!!)

Shift + Double Click: Mark entire loop as seam

Ctrl + Click: Mark shortest path as seam

Click + Drag: Draw seam path

Hold Alt using any of the actions above to clear seams