Trying to be mind numbingly accurate when trying to weigh bees with scales is a lot of faffing therefore hefting can provide a rough order of magnitude to the amount of stores a hive probably has at the point of hefting. Doing it regularly with your own bees and eqpt configuration you should notice hives getting lighter in weight as the bees devour their stores through the winter. The earlier in the winter they are getting lighter indicates the need for action. i.e putting fondant on. Some hives will take longer to consume stores the fondant goes on later its as simple as that. There will be those that come along and like to try and accurately weigh and thats up to them. Me, I prefer to be more productive with my time like others on here.
KISS... The objective is to calculate hive weight so as to identify when you need to feed to stop your bees starving........ simples.
My fifth winter, and hefting hasnt always been good enough, so I weigh my hives both sides it gives me more of a difinitive answer, and I can work out what I need to feed in turms of fondant /syrup etc..
I've colonys that are very frugal and by hefting I couldn't tell there weights, so weighing with luggage scales is a perfect and easy way to tell how heavy they are, I recommend and teach my mentorees to use scales as they can have a leason on learning to weigh empty boxes and then full hives.
The maths involved in working out how many stores a colony needs is very simple, and every new bee should be shown how to weigh with scales... I think gauging the weight of a hive by hefting comes with experience and even now I struggle to compare.
Using luggage scales IMHO is definitely a kiss method... Also I've found that most of the time one side of the hive weighs different to the other, some times by as much as 5 kgs.
Having a few colonys I need to know my weights for feeding, over feeding isn't an option, and could be rather a waste of time and money.
Just to illuminate... In the past I've over feed a colony which came out of winter a bit small and excess frames were removed to make space for the Queen to lay... About 40kgs was feed to a colony via syrup before the first full moon in Oct, I learned that over feeding can happen very easily and just ad lib feeding is OK if controlled to the required amount you need to feed.
Just my thoughts "good morning".