Dick,
I know of many offhand shooters that weigh their round balls but most use a standard measure for powder charges.

I am new to table shooting having just started a year or so ago. I recently had a table gun built and have started weighing all the balls sorting them out by .5 grain groups and weighing the powder charges on a scale so that all are exactly the same.

As a result I have seen more consistent, tighter groups. I think it is helping me. Anything one can do to make everything as uniform as possible gas to help.