For an active wordpress site the content gets bigger with time. Usually tou don’t even notice that until the site becomes slow and you install some caching plugin which makes the site to run even faster and you forget about the whole thing again.
Problem arises when you want to move your content with wordpress’s export and import tools. If you have a lot of content, the exported file which will be generated might be too big to be uploaded to the new server.
The easiest way to solve the problem is to split the exported file into smaller pieces using this splitter tool, and import each one of the generated files.