I use Visual Studio Online task board a lot for Scrum projects. But I do not like how much screen space it takes primarily because of lots of empty space.
So, I remove the empty space:
- I do not need the "To be tested" and "Testing" columns.
- The cards could be smaller with less margins and paddings
I use Tampermonkey to inject CSS into the page.
Just install the Tampermonkey Chrome/Firefox extension and use this script:
Before/After:


More info, less white (grey) space.
_happy_tampering()
PS: Once you have Tampermonkey you will see lots of opportunities to change the layout of web sites. You don't have to live with it. You can change it.
For example: a script which make visual studio build colors more pronounced to counter my red-green-color weakness: