Your memory controller won't handle the bandwidth of 1T;
Perhaps this will help:
The memory controller is like a doorway with a line of people going through. Like ticket takers at a sport stadium.
The doorway has an absolute limit on how many people can go through in any given time span.
Faster memory speed makes the line move faster.
More memory bandwith (1T) makes more lines of people.
Since the doorway is of limited capacity, people trying to go through too fast or too many lines of people will clogg up the doorway and piss off the people so they then decide to crash/lockup your computer or corrupt your hard drive.
The object of the game (for Intel and AMD) is to get as many people through the door way as fast as possible. Usually, with Intel DDR2 memory controllers, the ticket takers at the doorway are really fast, compaired to AMD DDR memory controllers. So speeding up the line (memory) is the most effective way to get more people through.
Since AMD ticket takers are slower, putting more ticket takers on the dorway (1T) works for AMD memory controllers.
That's not to say that with an intel memory controller you can't slow down the memory enough so that you could add more ticket takers, but that way there will still be less people going through than just speeding up the memory (line).
Some motherboards, due to their design, may be able to support higher bandwidth than others. Those manufactures with beter memory controlles just add the 1T option so that in case it can work, it's there.