DITA uses topic-based authoring to enable greater reuse opportunities. For example, these five publications share several reused topics:

You can also reuse a specific topic element, such as a note. For example, if there is a standard disclaimer or warning that is used in all product manuals, you can write the warning once and reuse it in other documents.

The level of reuse can become very granular; paragraphs and even phrases or words can be parsed and reused across topics.

There is a big difference between reusing content and copying and pasting content. When you copy and paste content, there are duplicate files with the same information. When the information is updated in one, the changes are not reflected in the other files. Reuse, on the other hand, stores content in just one file. When updates are needed, you can update that one file and other files reusing it are also updated. This ensures consistent documentation and reduces the time and effort needed to create and update content.