List of actions performed by "Optimize MP4" menu option

Is there any description on the list of actions performed by the Optimize MP4 context menu option?

I have just tested it on one of my current hundreds of MP4 files and I've seen that it has created a thumbnail for that video that it wasn't there before. Good! However, I am a little bit scared of any option in any program that is called "Optimize" without further clues on what it does. This kind of options have historically run some optimizations that some other software may accept or may start causing incompatibilities. So I would feel more comfortable knowing a little bit better what is behind it before using it massively with all the other hundreds of files.

I have checked the support documentation but I could only find a reference about where the metadata block is inside the file, and the benefits of having it at the beginning of the file instead of at the end. Sorry if the information is already somewhere but I could not find it.

Thanks in advance,
·· joan

...and now I see that mp3tag cannot show the thumbnail recently assigned to the MP4 video, so I even wonder if mp3tag has been really creating it, or if it was created by Windows itself as part of the save process.

see this thread from 2006:

"This function removes all "free" MP4-atoms and moves the "moov" and "tags" MP4-Atoms in front of the actual audio data. This reduces the size of the files and may solve some problems with not displayed tags in other programs."