Trim

Key K. Removes the extra piece of a line — up to the nearest intersections.

Before and after: a click on the tail right of the crossing removes exactly that tail.
Before and after: a click on the tail right of the crossing removes exactly that tail.

Click a segment and exactly the part between the intersections with its neighbours disappears. Drag the cursor and everything it passes through is trimmed: that is the fastest way to clean up a mesh of lines.

What it is for

This is how outlines are built “from layout”: first draw crossing lines and circles without caring about the boundaries, then trim away the extra. It is faster than aiming each segment exactly from corner to corner.

About constraints

Trimming removes geometry and with it the constraints that were held on it. So after a trim the degrees of freedom go up: the outline became freer and needs defining again.