When would an oblique cut be most appropriate?

Oblique signifies anything that is not at right angle to something. So, an oblique cut is one, which is not perpendicular to the side that it intersects.

In anatomy, an oblique cut refers to a diagonal cross-section achieved by slicing the part of the body or the anatomic composition, in any plane, which does not intersect it at a right angle, or does not parallel the longitudinal axis, that is, neither transverse (horizontal) nor longitudinal (vertical).