One of the most reliable uses.
WHY IT WORKS WELL
The material is in front of the model. It is transforming, not recalling.
Hallucination risk is considerably lower.
HOW TO ASK
"Summarise this in [length]. Focus on [what matters to you]."
Being specific about focus matters. A general summary covers what the document emphasises, not what you need.
USEFUL VARIANTS
"What are the three main points?" "What does this document ask me to do?" "What are the risks or obligations in this?" "What has changed from the previous version?" "Extract every date and deadline."
WHAT STILL GOES WRONG
Important nuance lost Qualifications dropped, so a hedged statement becomes definite Something the model judged unimportant that matters to you
WHAT TO CHECK
Anything you will act on, against the original.
For a contract, a regulation or anything consequential, read the relevant section yourself.
THE PRACTICAL USE
Summarising to decide whether to read the whole thing, which is genuinely valuable.
Not summarising instead of reading something that matters.