What role does astrology play in a devotees' life? Well, it depends on who you ask. My personal opinion is that astrology can be very useful, IF you have a good astrologer. In fact in Srimad Bhagavatam it states:
Whether one has a short life or a long life, one must suffer the threefold
miseries of material life. Therefore any gentleman, dhira, must be
interested in jyotisa, astrology (Bhag. 10.8.5)
But that being said in the Bhagavad-gita it also states:
"If you become conscious of Me, you will pass over all the obstacles of conditioned
life by My grace. If, however, you do not work in such consciousness but act
through false ego, not hearing Me, *you* will be lost" (Bg. 18.58)
So how to reconcile these two statements? Well, I heard something very profound that made a lot of sense to me. Astrology gives you an idea of the environment that you have to work with. But it doesn't mean that something WILL happen because there is always that Krsna factor that can change everything.
That once again puts the responsibility on you. I think sometimes getting an astrological chart done makes someone feel that "Ok, this is what is going to happen. I don't need to do anything." That is such a fatalistic attitude that completely disempowers an individual.
We always have free will and the entire purpose of material existence is to become educated. Educated that we do not belong here. The planets are simply teachers that help us in our education. If however, we learn our lessons voluntarily, then we do not need those lessons and hence sometimes those things that are predicted in our charts do not come true. There is no point in teaching someone something they have already learned.
So yes astrology is useful, but more important than astrology is self reflection and dependence on Krsna. By self reflection and association with devotees, Krsna will give indications of those things we need to work on whether it be cultivating humility to becoming a compassionate individual. If we voluntarily start to work on our anarthas, while keeping Krsna in the centre, then Krsna will personally help us. If, however, we want to learn the hard way then the planets will happily teach us by arranging for us to learn our lessons.