Your definition of damming is different from what I refer to as damming.

You are simply making the weld discontinuous in the corner, such as in the case of a base plate welded to a column shaft or stiffener to the flanges and web of a beam or girder. The discontinuous weld in the corner is not a bad practice when due consideration is given to the effects of residual stresses and how they are added as vectors. Even worse is the case where you have three intersecting welds at the intersect of the X, Y, and Z axis. This situation is the reason behind paragraph 2.8.3.4 in D1.1-2006. AISC also notes that welding in the "k-area" of columns should not be done (12-17, 1). This is also addressed in 16.1-363 of the 13th Edition of AISC Steel Construction Manual.

To go further into the discontinuous weld in the corner of a beam of column, the area of the radius is often work hardened during the manufacturing of the member when the tilt of the flange is straightened. This can result in a tendency to crack due to the reduced ductility and notch toughness in and around the radius between the flange and the web.

Damming in the context that I am familiar with is placing a "tab" at the end of a groove to prevent the molten weld metal from spilling out of the groove. It is an invitation to slag inclusions and incomplete fusion at the end of the groove. Some folks also place the dam at the end of a run-off tab with similar effects, but the incomplete fusion and slag inclusions are usually beyond the end of the weld joint and not as detrimental in the case of static loading. Weld dams are prohibited by paragraph 2.16.6 (Cyclic Loads) of D1.1-2006.

Best regards - Al