"Must"? What makes you think having twice as many entries would cause the program to do twice as much work? Does it involve that much more processing to run 10 cars in a race compared to 5? There are a lot of overheads that need to be done to say run a race, even if there no drivers in it. But this is irrelevant, what does it matter how big the log file is, provided there is sufficient disk space? And how does this affect stability of a program?

And something I just thought of - earlier copies of a new version often have substantial debug logging in, which can SUBSTANTIALLY increase the size of a log file.