You could use them to know what the text is about, and if it's worth your reading time. In this situation, it's fine if the AI makes shit up, as you aren't reading its output for the information itself anyway; and the distinction between summary and shortened version becomes moot.

However, here's the catch. If the text is long enough to warrant the question "should I spend my time reading this?", it should contain an introduction for that very purpose. In other words if the text is well-written you don't need this sort of "Gemini/ChatGPT, tell me what this text is about" on first place.

EDIT: I'm not addressing documents in this. My bad, I know. [In my defence I'm reading shit in a screen the size of an ant.]