I'm having a hard time cutting the grooves on the corners. I feel like there's a more precise way to do it than knife the 4 corners, but struggle with subdivide. Is there a better approach than knife?

Awesome thank you very much!

Thanks. A perfect example!

Thank you so much.

Thank you for this Explanation Jonathan!

A small addition to the solution from Jonathan: use Select Mirror to quickly select the similar faces.

P.S. I used the Pie Menu addon for the Pie menus. It can be enabled here: Edit->User Preferences->Add-ons->Pie Menu

Thanks

This is a cool shortcut, you could also after selecting the area instead of mirror you could select same perimeter, although your way is slightly faster

To quickly select the faces of all the corners simultaneously after you've subdivided, select the 3 faces around a corner, then:
Select -> Select Similar -> Face Regions
This will select all the additional 21 faces of the other corners in one fell swoop.

Then -to select all the insets of the cube at once, select one of the inset faces, then:
Select -> Select Similar -> Area

PS: I'm new to Blender and I'd like to know- is there a shortcut for the "Select" menu? I can see it becoming tedious having to move the mouse and actually clicking the Select menu item at the bottom everytime I need to.

so helpful!