I frequently want each frame in a player’s part (excluding the first frame) to have a fixed number of staves.
Dorico’s current setting of “Fixed number of systems per Frame” is great for certain types of full score, single-staff player parts (at ~10 systems per frame), grand staff player parts (at ~5 systems per frame), or other cases where the number of staves per system remains constant. However parts that have differing numbers of staves per system (String Section parts with complex divisi, vocal scores, large ensemble piano parts, Organ parts with pedal staff, etc.) are a bit of a pig to set up.
For example, a big band piano part may have a roughly equal amount of grand-staff (two-handed fixed material, or simultaneous Guitar and Bass cues) and single-staff (systems of rests, slashes or single-line material with/without chord symbols) systems, so choosing a fixed cast off value that favours one approach, will necessarily require many manual edits to prevent under/over-filling the frame.
On a similar note, the “Scale number of systems by frame height option” is a godsend in a lot of cases, but I find that how Dorico goes about filling the reduced space leaves a lot to be desired, especially if the reduced frame (eg. the first page of a flow) shares a 2-up spread with a full frame (last page of previous flow, or 2nd page of current flow), with Dorico either spreading too few systems over the space, or leaving a huge amount of space below the bottom system of the frame while jamming the top system right up against the top of the usable space. An option to align staves across a the two pages of a spread would go a long way to solving that, as this would make it so that the top staff of the smaller frame aligns with the first “available” staff on the other page based on the contents of the staff (eg. text and/or high notes might force it downwards by an extra staff, thereby avoiding collisions with stuff outside the music frame like Flow Titles and Composer Text.