Ideally, you should be able to fully compile your documents from a variety of modules. In practice, however, this will not always work, given that sometimes a text passage is really only needed once in a single document.
In this case, there are text passages that differ only minimally from product to product. This is annoying, but can be managed in many cases, as often these slight variations can be predicted systematically. For example, if only the product name or the label of a user interface element changes in the module for each final document. For systematic differences like these it is best to create placeholders in the modules. When the final document is created, the placeholders are then filled with the required variable.
The size of the modules should be as large as possible, because even though reuse saves time, it generates costs elsewhere. Each module must be found (and then managed) for the final document. However, the smaller the module, the greater the administrative burden. This can be illustrated with an extreme example: in principle, you could define each individual word of a manual as a separate module. The manual could then be assembled from these modules. However, the effort required to find the individual words would be much higher than the benefit you could get from reusing them. The same applies at all levels – the smaller the module, the higher the reuse rate, but also the higher the administrative workload. Usually, you will therefore end up with a module size of two to three paragraphs. However, there is nothing to be said against defining entire chapters as modules if they appear repeatedly in identical form in the final documents. This is the case, for example, with the instructions for disposal or the warranty conditions, which are used in (almost) the same form in all manuals. The ideal module size therefore depends on the specific document material and the reusability of the content elements.
Modularisation is a powerful tool for efficiently creating manuals. But it can also be useful to modularise other types of text. Before you decide to take this step though, you should check whether your own content is suitable for this. This is because even modular text creation involves some effort. This blog post will give you some initial tips for evaluating your content. In case of doubt, having it assessed by external content and modularisation experts can also be useful.