Yes and no. Kinda sorta.
If you have a pack that weighs 15kg, and you add 3L of water, you increase your pack weight by 20% and it's now 18kg. Which is A Lot. If I replace a tarp in that 15kg and save 300g, then I reduce the pack weight by 2%, add the 3kg of water and it's not that significant. *BUT*, if I have 10 items in that pack, and I shave 300g off each of them, I save 3kg. Enough for that water...
For perspective, my dry packweight (that's sans water, food and fuel), is 5kg. If I swap my 200g tarp for an 800g tarp, That adds 600g to my pack, and increases it by 12%. If I did that on every item I wouldn't be able to carry it...
Ideally I would not carry 3kg of water, at most if moving I'll tend to only have 1kg of water, I carry a water filter, and am acutely aware of where I might next find water. Just before I stop for the night, I may add an extra 500g of water so I can make a cuppa in the morning before I find my first source.
In any discussion of weight saving it generally looks really petty, shaving 200g here, 300g there. But it really adds up, I shaved 2.7kg by swapping from a Berghaus Vulcan to a Exped lightning 60. The lightning is just 40% of the weight of the vulcan. I shaved 700g off my sleeping bag, 800g off my sleep mat, and so on.
Three bags? Yeah, sod that. One pack on my back only please, and then if you picked it up you'd likely react "that's light". Each unto their own.
Horses for courses.
J