EDIT: Reading this back it sound confrontational which isn't my intention, but I genuinely want to know what you referred to because having used the A7s extensively there was very much a time and a place for them - and that time was 'whenever the FS7 was already in use'.
For me its three times:
Gimbal use
Moonlight shoot (or inside caves etc.)
Timelapse/starlapse when i need FS7 somewhere else.
Only times i use a7S as video.