I don’t know about you, but as a child, I was never satisfied by the argument that I really ought to eat my vegetables because there were children in some parts of the world who didn’t have enough to eat.
Not that I would want to overlook the fact that I was and am – along with most readers of this post – objectively among the luckiest cohort of people ever to have lived. (Zoom just a little way out historically to put our levels of comfort into some perspective.)
Of course, the thought of those less fortunate should give us pause to appreciate the rare abundance we have available to us.
That very abundance… The constant availability of more… is exactly why we don’t need to eat everything we currently have on our plate.
When you have more available to you than you need, you can afford to be picky*.
And so to Impression Share Lost to Budget… as this is a measure of how much more there is available than you need. Or to be more precise, a measure of how much more traffic there is available than your campaign – in its current form – is in a position to use.
And for all the limitations of Impression Share as a metric (the flexibility of the denominator in the equation… the obscurity around of what an ‘eligible impression’ is…) it is a good measure of the above.
In this short snippet from my course, Google Ads Level Up (from module 7, unit 1 – Optimising Bids) I go through why a high value for Impression Share Lost to Budget is – all things being equal – good news for your optimisation efforts.
*p.s. You should still eat your vegetables.