The failure it prevents is ordinary. Somebody taps a link in an email or a message, the app opens on its home screen, and they now have to find whatever they were promised. Most do not. Every campaign, every notification, and every shared link loses a proportion of its audience at exactly that step, and the loss is invisible because the tap was recorded as a success.
The variant worth knowing is deferred deep linking, which handles the case where the app is not installed yet. The person taps, goes to the store, installs, opens, and arrives at the intended destination rather than at the home screen with no memory of why they installed it. Without it, the entire journey from advertisement to installation ends in a shrug, which wastes the acquisition cost you just paid.
Implementation is a technical task rather than a marketing one, and it involves configuration on both the app and the web side so the platforms trust that your links belong to your app. It is not difficult and it is frequently skipped because nothing appears broken without it.
Test it the way a customer would experience it, which means on a real device in both states: app installed and app absent. Test from an email, from a message, and from a social post, because link handling differs by source and a link that works from one frequently fails from another.
Keep the web version of every destination genuinely usable rather than treating it as a fallback. A meaningful share of the people following your links will never install the app, and a web page that exists only to say the experience is better in the app converts nobody. The link should work equally well in both places, which also means the campaign continues to function for the audience who deleted the app or never had it. Record which link produced each installation as well, because a campaign that appears to underperform is frequently one where the destination was broken rather than one where the audience was wrong.