While I tend to agree that UI walkthroughs are not ideal in apps that rely heavily on gestures (a shortcut should almost never be your only interface!), I do think there are a few reasons you might still want to use them:
In today’s crowded app market, many users will just download a bunch of apps and take them all for a spin before deciding which one to stick with. If your intro screen / walkthrough can reaffirm two or three core features a user is looking for, they may be willing to spend more time checking out your app since they have a better idea of its capabilities.
Revealing add-on functionality
With many more complex apps now requiring hardware accessories or in-app purchases to unlock functionality, app developers may need to include a walkthrough to demonstrate the additional functionality to users who have yet to buy the additional requirements.
The Paper app is a good example of this, combining in-app purchases with brief demonstrations and demos of the additional pens and drawing tools that can be unlocked. In this case, the walkthrough screen lets new users first see and even try out the functionality before purchasing.
Walkthroughs should be used to explain broader concepts or requirements rather than gestures or individual features. If your app can’t be used without certain accessories, accounts or other preconditions, you might need a walkthrough.
If you’re explaining basic functionality or gestures, consider other ways to make the functionality discoverable first.