@epriestley As perhaps an example of another use case, in my workplace we needed, amongst others, the following lists of Maniphest tasks:

1. assigned to the viewer, regardless of the author,
2. authored by the viewer, without self-assigned,
3. subscribed by the viewer, without (1) and (2).

(1) is obviously trivial (there's already a built-in query), but the other two seemed to require custom "NOT" filtering. Of course, (2) can be solved to an extent by using "Group by assigned", but it's not very convenient. Because I tend to self-assign most of the tasks that I create, the ones that I have assigned to other people quickly get visually overwhelmed by the large group of "Assigned to kerberizer" (not to mention that with my username this huge group tends to get in the middle of the list).