SLOB is a nice dose of ZDDP and calcium. Unlike many of these additives, SLOB is not in a thick, goopy base oil. If you are inclined to run high zddp/calcium levels either for long drain ability or a high stress engine environment, it might be your ticket. Folks running old pushrod flat tappet engines with high spring pressures might also be interested in extra anti-wear additives.
It's not needed for most folks, truthfully. But when it was available on close-out for a buck or buck-fifty, it was a nice cheap way to raise regular PCMO motor oil additive levels to heavy duty levels. Certainly wasn't worth it's original $8-11 pricetag....but $1???