One of the most common mistakes made in digital media planning is the inability to prepare banners at the appropriate dimensions to the advertising spaces in the media.
Most media can accommodate standard ad sizes as well as different areas of their own. It is not wrong to say that the standards in banner sizes are determined by Adwords / Adsense. Adwords has been offering flexible advertising space to its users for the last 2 years, but it is still the most widely used advertising space. As you can see immediately on this page 728 × 90, 300 × 250 ..
Therefore, when creating ad designs on the display networks of Adwords and similar ad breaks, you should first prepare the most commonly used ad slots. If your workload allows you to prepare ad images of all sizes, you can advertise in all possible areas, it will ensure that your ad is displayed properly on the sites you run, and your cost will be reduced while getting high efficiency from your ad.
If you take a sample ad I just encountered on this page, you may see an ad 468 × 60 in the 728 × 90 ad slot in the image below. Although the 468 × 60 advertising fee pays 727 × 90, the space it occupies is much smaller, and so is the yield it is likely to receive.
Here, the advertiser’s banner does not work as one of the most commonly used sizes, 728 × 60, causing such a loss of space. If the ad’s smaller dimensions have not been prepared, it will probably also cause it to miss smaller and more square ad spaces.