While NCP Extension does not replace every need for IPX and SPX, there are some cases where NCP Extension can simplify the communication between the client and the server. The advantage of an NCP Extension is it uses the existing connection of the client, freeing you from needing to set up communication sockets. You can use NCP Extension in many of the cases where you are currently using IPX or SPX.
The disadvantage is that NCP Extension takes a connection. If your application isn’t already establishing a NetWare connection, and you don’t want to establish one, you may choose to use IPX and SPX instead.
Another disadvantage to NCP Extension is that communication must always be initiated by the client. With IPX and SPX the client and/or the server can initiate communication.