Depending on the arrhythmia and its frequency, the symptoms can be much more than being a just a problem in themselves, or diminishing the quality of life because the patient feels bad, and any drugs used to control the tachycardia are given just to placate the patient. I'd say the symptoms accompanying a frequent tachycardia ( such as my atrial tachycardia which before I took metoprolol would exceed 200 BPM, and my daughter's, which left her with a resting heart rate of 130, increasing to close to 200 with any activity) can well be indicative of compromised circulatory perfusion to any number of organs as a result of the tachycardia. Not to mention, of course, the effect of the tachycardia on the cardiac tissue itself, and tachycardia-related heart failure down the road if the tachy is not brought under control. Our daughter's EP informed us that if they could not bring her incessant tachycardia under control, she would die. She was prescribed an inordinate number of both anti-arrhythmic and rate control drugs but nothing worked for very long, she had a number of ablations, but the one that was finally successful was an epicardial approach via the thoracic cavity.

Symptoms associated with bradycardia are very important in determining the treatment of a patient with bradycardia. As the American Heart Association states in its guidelines for pacemaker implantation:

The term “symptomatic bradycardia” is used frequently throughout the guidelines and is defined as a documented bradyarrhythmia that is directly responsible for the development of frank syncope or near-syncope, transient dizziness or light-headedness, and confusional states resulting from cerebral hypoperfusion attributable to slow heart rate. Fatigue, exercise intolerance, and frank congestive heart failure may also result from bradycardia. These symptoms may occur at rest or with exertion. Definite correlation of symptoms with a bradyarrhythmia is a requirement to fulfill the criteria of symptomatic bradycardia.
https://www.ahajournals.org/doi/full/10.1161/01.cir.97.13.1325
Besides the ZIO patch testing I underwent to document symptomatic bradycardia, I was also quizzed pretty closely by both my EP and cardiologist as to the circumstances under which my symptoms appeared in association with the brady. They worried especially when might be driving, or operating machinery. The cardiologist asked me if I felt the symptoms ( light-headedness, slight shortness of breath) when I was resting, and seemed freaked out at my response-I didn't intend that! But my heart rate would often go into the high 30's when I was just sitting, and I told him "it felt cozy, like I could just go into nothingness, no thoughts, reactions, just nothing". Seems they had no problem recommending the pacemaker, with enough medication to control the atrial tachycardia, and now A-fib. It's worked very well for me, glad they didn't think I was a psych case that needed placating.