you can weigh your stave, but if the relative humidity is too high, it still may have too much moisture to make a good bow,, and would need to be placed in a dryer location,, and the opposite as well, if the relative humidity where the stave is stored is way to low,, the bow could break,, so a moisture meter can help in that way,, I had a bow explode this winter, I had it in a heated room,, of course it was not loosing any weight, but the moisture content of the bow was 6% or lower,, my meter will only go that low,, so my moisture meter gave me a clue not to keep bows in that room,,
it is not a necessary tool for sure,, but at times can be very helpful,, when you are roughing out a stave, the meter will give you a clue as to if the bow might check or not,, etc etc etc,,