I am surprized that someone out there aint making 3pce cues (ie with 2 lite-wt joints).
A stainless 5/16"--18tpi wood-to-wood joint (with a brass sleeve in shaft) probly adds less than 1oz to a cue.
U kood hav a 20" maple shaft (instead of 29"), plus 20" maple mid, plus 20" butt (instead of 29"), ie a 60" long cue (the extra 2" would help the balance).
A 3pce cue would allow a shorter cue-case (the only reason to hav a 3pce instead of a 2pce).
I hav three 2pce cue-cases 31", 32" and 34" long (I kood shorten one to 21"). In fakt a 20" shaft fits some office brief-cases on a diagonal.
I know of billiard players who now uze a 2pce instead of a 3/4jointed cue, koz a 2pce fits in their luggage.
A 3pce cue would fit in your flight hand luggage (but it wouldn't be allowed).
The main question iz whether a 3pce plays az well az a 2pce.
Heavy steel joints would certainly disappoint (ie too much energy loss), theze probly add 2oz each (or even 3oz) -- but a 5/16" 18 kan add less than 1oz -- and of course a pure wood joint would add allmost zero wt.
Apart from energy losses, joint wt would spoil balance (ie 3pce cues would be noze-heavy unless counterbalanced).
A heavy joint in the butt wouldn't hurt energy transfer much (hencely this joint kood be any type u like).
But a heavy joint 20" from the qtip would hurt energy transfer (and balance) -- here the joint would surely be near an anti-node for bending/flexing/buckling, and thusly rob energy. A heavy joint at a bending node wouldn't hurt energy transfer, but a heavy joint at or near an anti-node would. And anti-nodes nearer the qtip suffer a larger displacement than anti-nodes nearer the butt, hencely more energy loss.
Anyhow all joints hurt energy transfer one way or another.
A change in material leads to reflection and refraction of axial impact shock waves. Even a wood-to-wood joint would create reflection losses, and surface effect losses, koz of small (even microscopic) air gaps.
There are at least 4 major ways a cue bends (and vibrates) during impact.
Hencely there are 4 major sets of bending/flexing nodes and anti-nodes, and a badly placed joint might sin gainst 2 or 3 of theze.
Anyhow, a 3pce cue might be my next project -- a sneaky pete naturally.