I have to say, that SDS is really helpful especially is large clusters.
Pros:
1 - Less programming time
2 - Helps manage the systems more effectively
3 - In resilient sites, works really well.
Cons:
1 - I would read all the matrial you can on SDS, as it can be confusing
2 - Can get messing when starting it up, if you don't read up on it.
Wen to a site once where they enabled SDS, and included a blank 3300, and sent all the defaults to all the other fully programmed ones and deletes months of work all in a few clicks. Not to scare you or anythink.
Really, I think SDS is good and so does mitel as now by default it comes already enabled on 3300's.