Strategies and formations are also sometimes tested in the preseason. But we know that sometimes the formations that will actually be implemented in the actual season are rarely shown in the preseason.
I actually only see the preseason matches played by European teams just for fun, especially those who tour Asia and have a series of matches. They can field new players for the preseason match, but not with the actual game tactics. Because the tactics will usually still be adjusted to the strength of the opponents they study. Preseason matches are more about preparing the players' fitness before the official competition starts.