you don't have to have it, but it's nice if you do. I usually only use it if someone wants a copy of something and I have already dumped the DVD project. I always make a DVD master copy for myself so I use toast to make the copies from it. If you didn't have toast and needed to do that I suppose you could rip the DVD using a free ap and then simply drag and burn the VOB files to a DVD.....but toast is better.
I use toast all the time. It's actually a lot quicker for making multiple copies. SP4 only makes one copy at a time (unless I've missed something) and it starts from scratch each time. Toast copies from another disc much faster than SP4 formats each DVD.
Plus, it's great for copying back ups of your apps and CDs.
You don't NEED Toast, but it's worth getting. Toast will verify your discs, which DVDSP won't; it's also helpful for a wide variety of other tasks (backup, archiving, etc.).