Question: [iOS Human Interface Guidelines](https://developer.apple.com/ios/human-interface-guidelines/graphics/launch-screen/) say:

> 
> Design a launch screen that’s nearly identical to the first screen
>  of your app. If you include elements that look different when the app
>  finishes launching, people can experience an unpleasant flash between
>  the launch screen and the first screen of the app.
> 
> 
> 

The quote from [iOS Human Interface Guidelines](https://developer.apple.com/ios/human-interface-guidelines/interaction/first-launch-experience/) about **splash screens**:

> 
> Get to the action quickly. Avoid showing a splash screen, menus, and
>  instructions that make it take longer to reach content and start using
>  your app. Instead, let people dive right in.
> 
> 
> 

But Twitter still has splash screen and designers are ignoring guidelines writing articles [how to use branding in splash sreen design](https://medium.com/ux-power-tools/dead-simple-techniques-for-using-branding-in-ui-d44cb44e40ee?ref=prototyprio). 

What is their motivation and consequences on usability for ignoring these guidelines?

Answer: 
Maybe they are using other guidelines. You have the iOS Human Interface Guidelines, but also Material Design Guidelines. They are not OS-bound. Google applications on iOS also use Material Design. [Material Design guidelines](https://material.io/guidelines/patterns/launch-screens.html#launch-screens-types-of-launch-screens) for example talk about two kinds of splash screens.

> 
> A **placeholder UI** displays core structural elements such as the
>  status and app bars until the app has loaded.
> 
> 
> 

And

> 
> **Branded launch screens** display your logo or other elements that
>  improve brand recognition.
> 
> 
> 

We can't know for sure why they did what they did but the above mentioned **branded launch screen** makes sense for me. The rest of the Twitter application is pretty clean of branding.
I know that in some cases splash screens are a must due to technical reasons. Depending on how the code of the app is written, it may take some time for the app to load when launched so splash screens are used for that reason.