All purposes remain as personal judgments and deductions of muslims, the most important purpose is that it is a matter ordained by our creator who said in the holy Qura;an in Surat Al-Baqara. :-
2:184 (Fasting) for a fixed number of days; but if any of you is ill, or on a journey, the prescribed number (Should be made up) from days later. For those who can do it (With hardship), is a ransom, the feeding of one that is indigent. But he that will give more, of his own free will,- it is better for him. And it is better for you that ye fast, if ye only knew.
Benefits come from obeying His orders even if the benefits are not disclosed to us, the fasting itself is a test for the genuineness of our faith which deserve His reward.This is the first purpose in my view.