If a spiritualist is already perfect there is no fruit in studying astrology or doing anything besides constantly dancing, singing and discussing the All-Attractive Divine Beloved. The vast majority of spiritualists, however, are not perfect. They are human beings on the path towards perfection. Therefore the benefit of astrology for a spiritualist is quite similar to the benefit of astrology for any human being.
The benefit of studying astrology is that you will have a direct vision of the Hand of God. You attain this vision by understanding the clockwork within the mystical operation of the universe, and how the unfolding of time, measured by the motion of universal bodies such as planets, generates the conditions to fulfill the fates acquired by living beings as a result of accountability for their freewill. The more deeply one comprehends astrology, in theory and practice, the more vividly this vision of divine clockwork appears within the trees and clouds and cars and dogs and people of humdrum daily life. Eventually this vision intensifies into direct perception of the Hand of Godhead. It is a form of Godhead called “kAla” in Sanskrit: Fateful Divine Time.
Thereafter the spiritualist is left to use this vision as a catalyst for whatever particular spiritual proclivity or aspiration he or she may have. A karmi, for example uses this vision to perfect the selflessness in their dutiful responsibilities. A jnani uses it to better see the world through philosophical and objective eyes. A yogi uses it to better control the energies and powers in the world and the mind. A bhakta uses it to more deeply fall in love with the All-Attractive.
Since there is a gradation of perfection in selflessness among the above which culminates in the bhakta – the selfless lover of the Divine, we can therefore conclude that the ultimate spiritual benefit of studying astrology is Divine Love, although it is by no means assured that astrology will lead to this pinnacle. It can support it.