Why do I want a screen on my controller?

[NJ5]

Answer: I probably don't.

I can imagine some games will use it in a gimmicky fashion, a few games maybe even in a worthy fashion.

But in general I don't get why they didn't make it an add-on. The controller is huge and the screen doesn't look worth it. Even ignoring the fact that it might be expensive and use a lot of battery.