Streaming as the name implies is done when you have a huge file size. Straming downloads part of the file and begins to play it while the rest of the file is still downloading.
If you need a small sound file to react to a button or just to play when your file loads, then streaming isn't required.
However if large song files or dialogues for a presentation is required you will need to stream the file.
Streaming can be done to mp3 too by Windows Media if they are large. Windows media, Real Audio, Quick time all are capable of handling streaming. You have to decide a target audience and choose one of these 3 mojor streaming agents. More information can be found on the respective sites