Whenever you transfer (Wort to primary, primary to secondary, secondary to bottling bucket and bottling bucket to bottles) you want to transfer using a siphon, correct?
You want to use a siphon once the beer has fermented in order to minimize oxygen contact. Right after you've brewed, though, you need to aerate your wort. Many people pour from their boil kettle to their primary in order to get the wort aerated. Also, once in your bottling bucket, you can use the valve. There's no need to siphon from a vessel that has a valve on it...
I don't siphon the wort into the primary, but I do siphon the beer from the primary to the secondary and the secondary tot he bottling bucket. By not disturbing the beer before siphoning everything stays at the bottom and I get almost no sediment.