You better believe the weight that you loose in a hurry with diuretics/suana ... sure you can gain it back in a day (I personally gained 9 KG over night after the last BB contest I did) but you NEVER gain back enough strength ... not even after three or four days... trust me stregnth does not come back as quickely as the weight does!
There are a couple of issues with weight rebound. The first is how much weight is lost and in what manner, different methods will result in different physiological setbacks. The second is that it depends on what proportion of your bodyweight you are losing and regaining. The third is the level of performance required. Skeptic alluded to the last point; a boxer or someone requiring intense effort for sustained periods is completely different from someone who only has to waddle up and squat 3 times (to quote Wendler).