JeffTD
Senhor Testiculo
I'm not sure exactly what Jeff meant. (As in, I think he was replying to Marcus and explaining how it would put "stress" on the neck)
But, the truss rod puts counter tension on the neck to counter the strings tension. So in theory if you take off all the strings the truss rod is actually pulling the neck backwards. Taking off the strings for a bit and putting them back on won't make much of a difference, but if you leave them off for a long time you should consider relieving the tension on the truss rod.
Truss rod just keeps the neck straight, period. It works by counteracting string tension, but yeah... it's not gonna cause warpage unless you really leave it without strings.
To the dudes saying you only change strings one at a time... how dirty is your fretboard???