Each holiday offers us special lights for our well being and each has it's methods to attain those lights.
To benefit from the lights of SHAVUOT, men engage in Torah Study all night and specifically read תקון ליל שבועות (tikkun for shavout) which is comprised of Torah, Prophets, Writings, Midrashim and then proceed to learn Zohar and Kabbalah.
The Zohar below tells us that one who stays up all night and learns - NO harm can befall on him for the entire year. He is noted by G-d Z''A* for adorning NoK the Shechina - preparing her for the upcoming wedding on the day of SHAVUOT.
The Ari adds that staying up all night and learning removes one KARET or excision (being cut off from the light force on account of sin).
*Kabbalistic term for G-d