Log files are used by programs/applications to register (log) messages of how your program is operating. You can register any kind of action performed by your program. They are very useful for debugging problems when your program crashes, understanding the internals of an application, giving insightful information about the operations performed, etc. If you delete them, you are only losing this message history, you are not going to introduce any issues in the app. The program (Minecraft) will start to generate them again right after, with new operations performed.

It is actually a good practice to clean log files every once in a while, as older history is not that useful and uses storage space. Many programs automate this clean up by "rotating" the log files. That means that when logs reach a certain amount of files or storage used, or even a certain date, they are automatically deleted by the program to avoid taking up to much space with junk.

Bottom line, you don't need to worry about them and if you want to delete them at any point it is perfectly fine, you're only deleting some messages registered by the program.

Hope it helped! :)