Think of requirements as inventory or as component materials in a storage bin with a shelf life and a carrying cost. Inventory isn’t free. You have to pay someone to produce (model and document) requirements. You need a supply of good, current (fresh) requirements to produce a quality product.
There is no perfect, fits-all template or set of documents which will be effective across all companies or even for all of a given company’s projects. The business analyst should work with internal and external stakeholders to determine which communicative tools will best serve for each project effort and model requirements accordingly.
In addition to eliciting and specifying the requirements, an important part of the analyst’s value-add lies in helping business stakeholders and delivery teams identify and understand the constraints that will apply for the solution.
The simple fact is, you can’t know all the details upfront. You can and should, however, be able to work with your stakeholders to identify the broader range of necessary capabilities and constraints, or “placeholders for conversations”.