I know I've seen ideas for this before (actually I think I've submitted at least one myself), but it'd be really great if the adaptive grid snapping did a much better job.

If I draw a line in sketch (here on the grid), the next tool I take near that snaps to the line (good) but won't snap to the perpendicular grid (bad).
As it stands, I have to manually put in a perpendicular line starting from a grid point off the line, draw to the new line, and then use that either as a snapping target or a constraint.
It's good not to try to snap to everything but there are a lot of cases like this where things that seem like they should be obious snapping targets should work.