We find the vertex key indispensable in our workflows, generally split into two cases:
1. 'Eyeballing' the stroking of a contour/hydrographic line: To the experienced editor they can see for what scale vertices need to be added or removed, it's also important in stereographic capture. Seeing all vertices on a feature in a view extent (and comparing to similar nearby features) is important to judge whether the vertex interval should be increased or decreased a for given purpose.
2. When dealing with exact cadastral features, this alerts users that a surveyed point is either missing or need to be put in. Also where a node has been inserted that should not be there, i.e. two COGO lines with same bearing which would appear to be one straight line otherwise. With experience a glance of the vertices compared to the survey plan can show compliance to a fairly high confidence level. Extra vertices stand out like the proverbial.
In both these cases snap-level vertex display is not much use, as we look at all the vertices on the feature, and it is the overall context between them and the extent that is important. Snapping-level display is akin to exploring a cave using a lighter to see - you can only see one tiny part of it at a time, and can't compare one section to another.
Also in these cases, ornamenting the vertices or endpoints is impractical. For cadastre, it's not that bad but ugly especially once you start layering topological themes, but when it comes to contours you're talking millions and millions of points. Eeech.