One of the techniques I demonstrate in the video is using the iPad's multitasking environment to keep Freeform visible alongside another source of imagery.
That means I can research visually and build the board at the same time.
Safari references
When I'm researching through the web, the useful part of the workflow is reducing the distance between finding the reference and placing it into the project.
Instead of saving dozens of things into an intermediate folder that I'll eventually need to sort, I can decide immediately whether the image belongs on the board.
Using my own photographs
The Photos library is equally important. Mood boards don't have to consist entirely of somebody else's imagery.
I might include a previous photograph showing a lighting direction I want to revisit, a location scout, a test photograph, a colour reference or a behind-the-scenes frame that communicates something useful to the team.
Curate rather than collect
A useful mood board isn't the board with the most images. If two references are communicating exactly the same thing, I usually only need the stronger one.