The absolutely great thing about SONAR is how flexible it is with music creation. It's frowned upon (and for
many good reasons), but I typically record, mix and master all in one fluid process and have had some pretty great results from it.
Typically, yeah - I totally agree. Get the basic tracks down first and then start piling on the effects later during the mix, especially for things like synths that rely on low latency for live playing that PDC just gives you all kinds of headaches with.
But I like to be able to go back and make adjustments to the edit, or the raw sounds or anything I like, even at the mastering stage. Is the kick drum too weak? Well, I have the option of adjusting the mastering effects, or re-EQing / compressing the track itself so it goes into the mastering effects better (if I'm happy with everything else), or even replacing the kick entirely with a new sample, or - in extreme cases - getting a new part recorded that works better with the arrangement (pretty rare for that to happen by mastering, but it's nice to think that it's an option if you're entirely stuck).
In the case of the first test mix I tried DR on, this was already a completed mix/master that was convenient to have open at the time, which is why all of those effects were in the busses. I'd typically want to get the drums edited and (if needed) re-triggered/reinforced first before getting to this stage, of course.
That said though, Perfect Space is a great sounding reverb IMO, and it could really be a potential gotcha for people who are running it if they wanted to add a little ambience on the drums so they can get into the vibe while tracking other instruments. Ordinarily for live-tracked stuff it wouldn't be an issue, but softsynths and now obviously DR as well, this is a big thing to consider!