question on simple transcode

hi Intel,

OS: Ubuntu 12.04

       mediasdk-tutorials-0.0.3

       MediaServerStudioEssentials2015R6

Platform:  i5-4570S

Q1.  I found following and the question is below

        // Decode a frame asychronously (returns immediately)
        sts = mfxDEC.DecodeFrameAsync(&mfxBS, pSurfaces[nIndex], &pmfxOutSurface, &syncpD);
        ...
        ...   ==>  why  session.SyncOperation(syncpD, 60000) is unnecessary ???
        ...
        // Encode a frame asychronously (returns immediately)
        sts = mfxENC.EncodeFrameAsync(NULL, pmfxOutSurface, &mfxEncBS, &syncpE);
        ...
        sts = session.SyncOperation(syncpE, 60000);     // Synchronize. Wait until frame processing is ready