The prayers of the holy prophet, the Imams and Hazrat Mahdi (a.t.f.s.) have common and absolute effects in this world as well as the hereafter. This is because, from the viewpoint of Islam, this world and the hereafter are not separated from one another. However, one should be careful to note that none of the works related to physics and metaphysics are ineffective in this world particularly so the efforts and endeavours of Hazrat Mahdi (a.t.f.s.) who is the most perfect human-being. The Imam and the All-Wise Allah’s ‘Hojjah’ (who is also wise) will never perform any useless act. All their actions are effective and aside from leaving its effect in their own worship, they have their influence on others too. This matter bears numerous and precise evidences which can be seen in the history of Imams. One of the responsibilities of Imams (a.s.), in general, and Hazrat Mahdi (a.t.f.s.) in particular is the responsibility of praying for the Shias. In their invocations and supplications, they aren’t neglectful of praying for their partisans.
At times of hardship, they have prayed for them and solved the greatest of their problems. The story of Sayyed-ibn-Taoos is well-known when on the footsteps of the holy ‘Sardab’ in Samerra, he hears at dawn the pleasing voice of Hazrat Mahdi (a.t.f.s.) saying:
“O Allah! allow our Shias to live during our reign and glory.”
Also, in one“Tauqee” , Hazrat says:
“We pursue for their protection and pray to Allah (so that) our partisans’ hearts are at ease and comfort.” 
Another point: Not only the Imams’ prayers are effective and responded to, but, as per divine teachings and Islamic evidences, the prayers of others too are influential and answerable. For instance, prayers of an oppressed for his helper, prayers of parents for their children, prayers of virtuous children for their parents and prayers of a believer for another believer. Aside from the responsibility of leadership, Imamate and Prophethood, the prophet and Imams bear the responsibility of being the father of their nation.
“I and Ali are the two fathers of this nation.”
Therefore, their prayers for us (being their spiritual sons) are effective and responded to.
Besides, the more perfect the spiritual state of the one praying, the more effective are his prayers. The effectiveness of each one’s prayers is diverse. The loftier a person the more supreme are his prayers. Similarly, the more superior a person’s servitude and worship, the faster are his prayers answered. So the prayers of Hazrat Mahdi (a.t.f.s.) [who is the most perfect man and the ‘Hujjah’ on the land] are never left unanswered. Many of the bounties we receive are the result of Imam’s prayers.
As such, it’s worthy to prepare ourselves to attract our Imam’s prayers because the chances of their prayers being answered are very high.