surely if it was ‘Bad’ they would be suffereing additional stress/fatigue and wouldn’t be particularly quick as a result.
From what I can understand of bike fitting for TT/Tri bikes it’s all about how the body is supported on the bike in that ‘optimal’ position;
Riders torso is sort of suspended between your hips and sholders, ideally as flat/straight backed as possible, for a TT/aerio position upper arms supporting in as close to a vertical as practicable so weight is borne by your skeleton rather than tensed muscles/tendons, you ideally want as little wasted energy as possible which means if you can relax muscle groups in the torso, arms and shoulders you are improving efficient use of energy at the same time as reducing frontal area then its win, Win…
Sensible leg angles are also important one as well though are they not? torso to upper leg and the range of angles the knee has to move through need to be ‘Optimal’
all in theory at least, in practise there are bound to be compromises…