Originally the thicker butt or tapered handle was to get the balance correct for the cue.
Thanks for the input, conetip! Your post is a real eye opener. If, indeed, the thicker butt/tapered handle was incorporated for the purpose of cue balance, then to me it is inconceiveable that modern cuemakers don't dispense with this cumbersome shape, and use modern techniques/materials for balance instead. Functionality in a cue is supreme, I believe, and looks are secondary. Obviously, others see this differently, including the majority of cuemakers.
Conetip, based on your numbers, and measurements of my butt, you must have a steeper-than-normal taper between the joint and balance point of your cue. That way, when you start the cylinder there (at balance point), it's diameter is roughly 29 mm. My (production) butt diameter at approx 18 inches from the end is 25-26mm, so if I use your 29mm number I won't have as long a cylinder. Another question, please: Do you consider your hands to be large, medium or small (just trying to second guess how 29mm relates to hand size). I'd say mine are medium and I'm tempted to cut a 27mm cylindrical butt end. Any warnings - too small???