Actually, thinning lugs near the shorelines not only gives them a more finished appearance, but also reduces stress risers where the thick lug material abruptly stops at the shoreline creating hard points. Thinning the lug near the shoreline at the points mitigates stress risers.
Lugged Steel Frame Construction|Wikipedia
Originally Posted by Wikipedia
In most lugged steel frames, the lugs have a simple pointed shape. The lug's curves maximize the strength of the joint, while minimizing the possibility of stress risers, which would otherwise make the frame prone to cracking at the end of the lug.
At increased expense, frames may have lugs which are cut and filed by hand into fancy shapes, both for slight weight savings and as a display of craftsmanship. In addition many frame builders file the lugs to thin them, in order to reduce stress concentrations. These ornate or fancy lugs may be painted to accentuate their appearance.