You can configure Yammi's settings via the menu: Settings -> Configure Yammi.
Only some options are explained here, the rest should be self-explanatory if you read the provided tool tips (stay over an item with the mouse for a while).
These settings determine, whether Yammi modifies the meta info in your files or renames or moves them when you change any attributes (eg. the title or artist) in the song info dialog.
When enabled, Yammi will immediately save all tags to the file (if possible) after altering any attributes in the song info dialog.
When enabled, Yammi will by default correct your filenames (if necessary) to keep the filenames consistent with the configured filename pattern after altering relevant attributes in the song info dialog.
When enabled, Yammi will by default move your files (if necessary) to keep the directory consistent with the configured directory pattern after altering relevant attributes in the song info dialog.
If you don't want Yammi to touch your song files in any way, you should leave these three settings disabled!
However, for easy organizing your song files I found it extremely useful to have consistent filenames, directories and tags at any time.
See also "Checking consistency" in "Advanced topics".
This value determines, how many items of one group must be present for a subfolder within the folder Artists/Albums/Genre/Year to be created. If you set this value to 1, every artist/album/genre/year will appear as a subfolder, a value of 10 only will create subfolders for artists/albums/genres/years which contain at least 10 entries.