Conditional lines on part cylinders

[Philippe Hurbain]

If you add a tangential face to the cyli, then the control point matches this face.

It also works if you join too partial cylinders together, as those side condlines complement each other. So for most usages, these condlines are OK and avoid the hassle of creating them.
It's only when you join to a surface not tangent that you need to add another condline.