A keyboard shortcut for "Collapse all" or "Expand all" would be very helpful. 

I have put in a request for this shortcut as well.

In case this helps anyone, I use Filters to achieve this.  The way it behaves seems to be that no matter the state of the Collapes/Expanded is for rows, it collapses all rows then applies the Filter and Expands all related (filtered) rows.



So the important column to have for pure Collapse/Expand functionality is what we are calling Level, which is =COUNT(ANCESTORS()) which resolves to 0, 1, 2, 3 etc. where 0 is the highest level.

So in my case with a bunch of Projects under a Portfolio, I can filer on Level=2 which really means in my case all Projects, Level=1 is Portfolios Level=0 is the whole sheet summed to the highest row etc.   This means I can make the Filter names more meaningful like "Major Portfolio Levels", "Project level" or "Projects + Task Level"

0

 --  1

 --  1

 -------- 2

 -------- 2

 -------- 2

 --  1

Just found that https://community.smartsheet.com/discussion/expanding-and-collapsing-hierarchyoutline-levels has a similar resolution.  There are gems in Community boards, but it takes hours to find them....

Right click on the Primary Column...Expand All/Collapse All 

Even better would be a simply tick option on filter for collapse after filter applies, otherwise expand... similar to the show father option