Jeroen,

"Options = Optional" : by default, it is required to have a resource assigned to each node of the service definition before a booking can be confirmed. With that property,  a booking can be confirmed without having a resources assigned to that node

"IsProfileInstanceOptional = Yes" : by default , selecting a profile instance for each node ( or connected interface ) is mandatory to be able to confirm a booking. To make the profile instance selection optional, you need to use that property

"Options = Hide" : this will hide the node in the booking wizard. You then need custom logic (custom script ) to assign a resource in the background in case the node is mandatory.

"HideIfResourceAvailable = Yes" : this will only hide the node if there is a resource available and automatically selected for that node.