There are many blessings to be had when we send peace upon our Prophet (pbuh). The Prophet (pbuh) will reply to our salaams. 

Abu Hurayrah (May Allah be pleased with him) reported: The Messenger of Allah sal Allahu alayhi wa sallam said, “There is not one of you who sends his greetings upon me except that Allah returns the soul to my body (in the grave) and I return his greeting.” [Abu Dawood, Saheeh Al-Albani]

اَللّٰهُمَّ صَلِّ وَسَلِّمْ وَبَارِكْ عَلَى سَيِّدِنَا مُحَمَّدٍ وَعَلَى اٰلِهِ كَمَا لَانِهَايَةَ لِكَمَالِك وَعَدَدَ كَمَالِه

Allahumma salli wa sallim wa baarik `ala Sayyidina Muhammad wa `ala aalih kamaa laa nihayata li-kamaalika wa `adada kamaalih. O Allah! Grant salawat on the Prophet without end on the number of perfection with which You dressed him!