This will always depend on the issue. A simple fault report need only be a page, summarising where and when the fault occurred, and how it has been remedied. Some reports, however, might extend to hundreds of pages.
A report could, for example, be part of a bid for a project lasting decades that has to meet complex technical specification and legislation.
In both cases, documents might be on file long term as a crucial record, so the writing must be clear, concise and precise, referencing who did what and when.