When drawing schematics to a A4 paper, in mm, I often find myself troubling with the following:
- When zooming in, It is most practically that the smalest grids are 0.25mm (major grid space 1mm and minor grid space 0.25mm).
- When zooming a little more out - the most practical grid settings would be major grid space 1mm and minor grid space 0.5mm.
- Then, 5mm / 1mm
- Then 10mm / 1mm
- Then 10mm / 5mm

It troubbles me because I can only choose one multiplier between major/minor grid distance - and making multiple grids is ineffective because # button turns every grits on or every grids off, only.
The use of multiple grids as it is today, doesn't offer an efficcient way to toggle between them (must open Document property menu and then multiple mouse click from the user, this is very ackward way of doing it on a small display laptop)

Therefore I want to suggest the two following solutions:

Solution 1 - the simplest one - make the # key toggle between multiple grid
Assuming only 1 grid, then it will work as default.
If there is multiple grids, say grid1 and grid2, then the # button should have the following effect (initially no visible grid):
1: grid1 is visible, 2: grid2 is visible, 3: no visible grids
There shouldn't become a situation wher 2 grids are visible at the same time by pressing # toggle key.


Solution 2 - Each grid can have a rule of what zoom level is required for it to b visible
This idea I have from a map (google maps amongst other) that view different levels of details depending on the zoom level. Professional map software (ok, I dont know the english term for this) often have different layers (houses, fences, poles, rivers, soil types, etc..) that for each layer can be set to be visible within a zoom range.


weird semi solution - confined grid

What?
Have thaught this off during drawind. What about have a grid that is confined inside a object - e.g. a rectangle ?

Why this may work?
This is maybe one idea that make sense for me only and nobody other, so let's me elaborate a bit.

When drawing things like a connection line diagram, I often uses rectangles to represent an object with multiple connectors. Then I need to place small text and symbols inside that box that need a grid line settings 1mm / 0.25mm, while outside the box where the bigger wiring is drawn, it make sense with a grid settings 10mm / 2mm (or something slightly different depending on type drawing)

Possibel Caveat (things not thaught through)
User must choose if grid offset to bounding box or to a corner (if rectangle) - and what should happens if that object rotates.

almost a million years ago I offered this file for users to have a multiple grid system that appears and disappears as one zooms. Of course your requirements are much more precise but I thought other folks might like this arrangement, at least to try out. if they like it they can make it their default...