Originally Posted by FBinNY

You often can't use pitlocks with rear horizontal dropouts because they lack adequate clamping force. (depends on a number of factors so it may me possible if you're not a strong rider).

The front with discs is a more complicated question. Suspension forks (varies by fork) sometimes have some slop in the vertical movement of the struts. This can cause the axle to be worked as if held between two hands that are moving with respect to each other. That process can either loosen the nuts, or cause the axle to walk down the dropouts (or both). The safety lips do a decent job preventing loose wheels from coming off unless a seriously loose wheel is ignored until the nuts have fallen off.-- Side note, I file those off all my rigid forks, but would never remove them from a suspension fork.

The disc brake question depends on the brake. If the brake is forward of the axle the action of the brake on the disc levers the axle upward, or deeper into the dropout. This is good design. OTOH if the brake is behind the axle, the braking moments push the axle down or out of the slot. Again, safety lips act as a safety net, but generally any decision about using pitlocks with disc brake hubs depends on where the brake is.