Amavisd has 3 levels:
1) Spam tag level: This is the level where information about the spam status is added to the header. You can set this to a low level like 0, as no actions are bound to that level.
2) Spam tag level 2: This is the level for tagging a email as spam. So thi score is the relevant score for moving spam to the junk folder.
3) Spam kill level. As the name says, spam with a score above that level will get deleted.