Here is a very minor caution which should not affect most RM users most of the time.
The way RM manages media files (including such things as the Fix Broken Links tool) depends on every media file used by RM having a unique name, distinct from every other media file used by RM. That sounds obvious enough, I suppose. But from the Windows perspective, for example, lots of different files on your computer can have exactly the same file name provided they are stored in different folders. Indeed, if you have different files in different folders which have the same file name, it can confuse the Fix Broken Link tool in RM. It might point RM to a file that has the right file name but which is not in the folder in which you intend.
To that end, the Fix Broken Links tool has a feature whereby you can tell it the location on your disk where it is supposed to look for the files with the broken links. And even if you don't have different files in different folders which has the same file name, it can speed up the tool considerably if you point the tool at a folder structure containing the files with the broken link. Otherwise, the tool might have to look at your entire hard disk which could take a very long time.
The way your disk files are arranged where a folder got too big and all you wanted to do was to split it into sub-folders is perfect for the Fix Broken links tool.