WE57 - for inbound transactions, outbound transactions, or both?

Hello,

Can anyone tell me if WE57 is used for inbound transactions only or is it used for both inbound & outboud? It seems in the documentation I have looked at, it states it is only for inbound. Why, then, when I try to create a new entry in WE57, does it ask for a direction (inbound or outbond)?

Any help would be great because I'm getting confused...thank you!!