Depends upon what are you trying to do....
. If the power supply is a perfect DC voltage source (that is, it gives the same voltage no matter what happens), the op-amp’s output would be solely governed by its inputs. Since there are no ideal voltage sources in the real world, you have to worry about the power supply’s quality if you want the best performance from an op-amp
if you are making operational amplifier.... Real operational have some imperfections compared to an “ideal” model. A real device deviates from a perfect difference amplifier. One minus one may not be zero. It may have have an offset like an analog meter which is not zeroed. The inputs may draw current. The characteristics may drift with age and temperature. Gain may be reduced at high frequencies, and phase may shift from input to output.
for audio application gain of the amplifier is important... A typical op-amp has a voltage gain of around a million so Clearly, there is far more gain than we require, so we must "throw away" gain using a technique called negative feedback.
If u are making schmitt trigger or so....resistor value calculation and hysteresis gap becomes important parameter