At one point, the search giant employed a full-page interstitial to encourage mobile web Google+ users to download and install the company’s Google+ app. On the surface, the results appeared to be good.

9% of visitors to the interstitial page clicked on a “Get App” button. But those clicks came at a cost. A whopping 69% of the visitors abandoned the Google+ experience when presented with the interstitial.

Google replaced the full-page interstitial with a Smart App Banner, which alleviated the drop-off caused by the interstitial, and ultimately retired the interstitial completely because it clearly wasn’t capable of producing the intended effect.

Now, Google is sharing a message based on the lesson it learned: ”we…hope that you will reconsider the use of promotional interstitials. Let’s remove friction and make the mobile web more useful and usable!”

Interstitials die hard

The user attrition Google saw with its interstitial probably won’t come as a surprise to many. Interstitials are widely considered to be among the most annoying ad formats in use. So why do companies continue to use them to promote their mobile apps?

The significant costs of driving mobile app installs is one of them. For companies that have a mobile web experience, placing interstitials and other ads on owned mobile web experiences looks like a great free promotional strategy. But Google’s experience highlights the fact that this strategy can be far from free.

Unfortunately, companies that only look at clicks and conversions will miss the attrition side of the equation and continue to market their mobile apps using ad formats that can be far more costly than anticipated.