Downweight

Underweight is a term used in ad optimization. This is done to reduce the number of ad impressions on underperforming placements and increase the overall effectiveness of the campaign.

The opposite of underweight is overweight, allocating more budget to more effective advertising space.

Example without weight

The announcement of a revolutionary new type of cheese is published on 5 different websites. A month later, the ad budget is revised and the following results are reported for the 5 websites:

Conversion rate = 3.4%Conversion rate = 2.2%Conversion rate = 4.7%Conversion rate = 4.1%Conversion rate = 5.2%

Remark. Needless to say, these results are not true. We apologize to all these sites if they are legit.

To improve conversion rates, and they are underestimated, which means shifting the budget to better performing sites. In this case, it would probably have been canceled completely and at the very least a smaller budget would have been allocated.

So your conversion rate will (almost certainly) improve simply because less money is being spent on underperforming sites.

Best advice

If possible, notify the site of poor performance before cutting your budget. Often, the risk of losing money makes a website pay more attention to its campaign and look for ways to improve its performance. It works twice as well if you share your goal with the site so they can focus on something.

7 ways to think about being underweight

Don't waste money on bad ad placements.
It's not just for websites, you can narrow the list down by category, time of day (or day of the week), and device. EVERYTHING that doesn't work properly should have a lower budget.
Before you cut a website's advertising budget, let them know they're not effective. It's amazing how the threat of money loss can (sometimes) affect your work.
This is one of the easiest and most effective ways to optimize your ad campaigns.
For example, before reducing your site's advertising budget, consider adjusting your ATF placement targeting or adding frequency caps.
Undercutting works best when applied in as much detail as possible (e.g. don't stop ads all over the site, only stop ads on pages or sections that aren't working).
Popularly known as getting rid of from an ad campaign.