I weigh Japanese greens just about each time, and since I am brewing Japanese greens most of the time, I am also weighing most of the time. I could probably get pretty close w/o weighing, but there is a bit of a mad scientist in me that likes to fanatically weigh things down to the .01 of a gram.
There is an added benefit to weighing, less waste for Japanese greens, more sessions per bag.
Most other teas I do not weigh, unless it is a new tea or maybe conducting tastings, etc.
About to go weigh a Japanese green to start the TD.