I have my theories about why Triple H was drafted to Smackdown, and then immediately traded back:
1) To balance the rosters. If you look at how many people were on the Raw roster versus how many people were on the Smackdown roster going into the lottery, Raw had at least a dozen more people on its roster than did Smackdown. Even today, I count 53 on the Raw roster (whether they're still active or not is a different question) vs. 44 on Smackdown. It was a way of getting Booker T and the Dudleys over to Smackdown without having to make a complicated storyline out of it.
2) To put HHH over. Since he finally realized that the fans don't want to see him bury everybody on the Raw roster (i.e. he has to lose some matches), he needed to be put over in some way to compensate for his recent loss to Chris Benoit (and now, Shelton Benjamin). Emphasizing his importance to the Raw brand did just that. While it arguably makes Booker T and the Dudleys look less valuable in the process, it still gives those guys a chance to get out of their rut on Raw.
To take a stab at your question, Woodifvh, I'm guessing that the internet rumors surrounding Brock Lesnar working a program with Taker were true. Since Lesnar left, WWE probably doesn't have a plan for him any more (short-term, of course). To be honest, I don't feel that he fits in on Smackdown any more. They're working to build new stars and re-establish bigger stars who have been ignored, and having Taker squash any of them right now would be a fatal mistake. I wish they would have traded him to Raw in exchange for Test, Lance Storm, and Scott Steiner. That'd help to balance out the rosters (once Steiner returns from his injury), and those three would fit in better on Smackdown anyway (especially since they all need some major career revamping - which fits into Smackdown's current plan). Just my two cents, though.