How do quasars affect us?
Quasars are too far away to affect us directly.
Quasars are very distant objects, millions to billions of light years away. So, even though they produce vast amounts on energy, the amount which reaches us is insignificant.
In fact even if the supermassive black hole at the centre of our galaxy where to ignite as a quasar, at over 25,000 light years away we would not feel the effects.
The fact that quasars are so distant means that effectively they are fixed points in space. In order to measure the positions of astronomical objects to great precision we need a fixed frame of reference. Positions of objects are often defined in terms of the J2000 epoch. This requires knowing the exact orientation of the Earth as it was on 2000-01-01 12:00:00. Quasars are used as fixed reference points to achieve this.