Whether for production efficiency or construction manpower, the total count of villagers not currently assigned to a workplace is key information at all stages of the game.
A single easy-to-glance indicator would be a great quality-of-life improvement over having to repeatedly scan and sum up the 2nd, 5th and 8th numbers across an array of identical values.
Would be helpful! In the meantime, I recommend holding alt and scrolling to wheel to quickly have a glance at what workforce is currently unassigned. I found it more convenient than scanning the upper left corner of the screen. Just look at your mouse and sum the numbers.