Option to restrict order size on an instrument based on individual needs

In order to avoid that a trader accidentally opens a too large position for his needs.
Every instrument should have a setting to restrict the max selectable position size.

For example a trader that is used to trade FX and irregularly trades gold might out of habit accidentally 
opens an order with the same size which would be way to big.
In order to restrict that, a setting to set the max position size for an individual instrument would eliminate that risk.