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.
Preseason game is not one to take to heart as some people does so I prefer it as fun just like you did said because of a truth these teams will not be putting in all of their very best, they do not really stand to gain much from the game so why stress much if not to test strategies and tactics which will eventually be modified. This is why when I see a team mostly the big ones winning almost all of their preseason game, I just see it as them exhausting themselves whereby they should be resting awhile and bring the actual performance to the main season.