Among the things AI tools are now routinely useful for, summarising a long document is one of the most immediately practical for a small business. Contracts, supplier terms, tender documents, insurance policies, regulations and lengthy reports all arrive in the ordinary course of trading, and all of them take time that a small business does not have. Handing over twenty pages and getting back a readable account of what they cover, in plain language, genuinely saves an afternoon, and it lets somebody decide quickly whether a document needs proper attention or merely needed to be understood. Used that way, for orientation, it is a real gain and there is no reason to be precious about it.
The limitation is worth stating precisely, because it is not the vague warning that the tool might be wrong. A summary is, by design, an account of what a document mostly says - its shape, its main provisions, its general drift. The parts of a document that cost a business money are very often not what it mostly says. They are a single clause about what happens if a delivery is late, a notice period buried in a renewal section, an exclusion in a policy, a definition that quietly narrows what is covered. Those clauses are short, they are exceptional by nature, and a good summary of the document as a whole may quite reasonably not feature them at all. The summary is not wrong; it is answering the question it was asked, and that question was about the document in general.
This suggests a way of using the tool that gets the benefit without the exposure. Use the summary to understand the shape of the document and to find out where things are, and then go and read the specific parts yourself, in the original. Better still, ask directed questions rather than only asking for an overview: what does this say about cancellation, about notice, about price changes, about liability if something goes wrong, about what happens at the end of the term. Pointed questions pull out the exceptional clauses that a general summary smooths over, and they turn the tool into something that helps you find the important paragraph rather than something that stands in place of reading it.
The sensible rule, then, is about consequence rather than length. If a document merely needs to be understood, a summary may be all it ever needs. If a document is going to be signed, or relied on in a dispute, or used to decide something expensive, the clauses that matter get read in the original, by a person, and where the stakes justify it, by a professional whose job that is. AI has changed how quickly a business can get to the point in a long document, which is a genuine improvement over not reading it at all - the outcome many small businesses were actually choosing before. What it has not changed is who is responsible for what the business signs.