The admin can decide if the single order amount over a certain limit must be marked as a potential fraud check.
For example, you have a shop with very cheap products and the maximum order amount that a “normal customer” usually places is about $20,-.
Based on that, you decide to set the threshold to $35,- (Amount limit).
If a customer visits your shop and places an order of $50,- it will be marked as suspicious.
You can find the rule weight settings on this page of the documentation.