You can report a few of their posts, and include a message in the report field that they have multiple bad posts. If it isn't obvious then you could just report all of the messages you consider low value posts. However, if you are asking what will happen to user with low value posts being that of the majority of their posts then that depends on the moderator dealing with the user. If they deem it bad then they may request a global moderator/admin to ban the user. Really depends case by case.