Rudrabhishek Yagya is an exclusive Yagya performed to please the Supreme deity Shiva and get his blessings. Rudra means Shiva and Abhishek means ritual bath. So, the literal meaning is the ritual bath of the holy Shivling. Shivling or Shiva Lingam is a divine structure that is strongly believed to be another form of Lord Shiva. In this Yajna, Lord Shiva is worshiped in his Rudra (furious) form.
Rudrabhishek Yajna involves the chanting of the 200 verses of Rudra from the Yajur Veda and in the Hindu religion, this Yagya is a very important act for pleasing and getting the divine grace of Lord Shiva.
Since Rudra Abhishekam involves many rituals, and if done with good intentions, this surely generates the maximum outcomes.