If you are happy with the results, then why bother with another program (compressor)? Compressor will give you a TON of more options for your export than DVDSP will. With DVDSP, you are pretty much limited to your bitrate and whether it is constant or progressive. I find that I have gotten better results using a CBR at about 5.5 MbPS.
But if you are trying to export for anything other than DVD, (say ipod, web, e-mailable quicktime, mpeg 1, etc…) Compressor is your boy!
I personally prefer to use compressor when authoring a DVD over DVDSP, but do what works for you.