Yes, water weight is a big advantage, because basically you're sucking out every last bit your body can and than put it right back in, it is a science, a trick
So you got a guy like AJ, he is 'walking around' in the 220 lbs range while training, maybe more, terms like 'walking around' weight vary, but lets just use something like that, he can be as high as 230 or more when not fighting
Than you have other guys who are walking around 200 for getting ready to cut to MW at 185, these guys are much smaller than someone like AJ, but I dont want to single him out, a lot of guys are huge, but he is trying to take it a step futher, It's just more of a lack of discipline for him than others, others make weight pretty easily
That 'water weight' can give some guys 10 or more lbs on the other guy, it was more noticable in the older days where guys like Tito used it as a major advantage, he woul come in around 225-230 lbs for a fight where he weighed 199 lbs at the weigh in
Frank weighed in at 197 I believe with clothes on and stuff in his pockets, he had 30 lbs on Frank, than fights afterward you can see the size difference between him and guys like Tanner and whoever else
The reason these guys are doing it and almost killing themselves is because its a major advanatage, thats why the foreign fighters do no fare well in the US, they are just not big enough
BUT, some guys it hurts because they don't do it 'the right way' or there body shouldnt be doing it, THE REEM at 205, AJ and others who always gas or just cant make it, Diaz was another one who did not perform as well at 155 as he does at 170