Why is Jesus called "Son of Man" in the Gospels? What does "Son of Man" mean and why is it used so often in the Gospels?

In the scriptures, the title "Son of God" is used in many different senses and is, paradoxically, more vague than the title “Son of Man.” “Son of God” can be a title of Israel itself (Ex. 4:22; Hos 11:1), of the Davidic King (Ps 2:7) and of the angels (Gen 6:2), all humankind, all the just and peacemakers are called sons of God (Mat 5:9), and so forth. 
 
In view of the ambiguity of the term, this is why Jesus did not simply say, "I am the Son of God." Rather, he spoke more clearly, saying for example, “The Father and I are one… to see me is to have seen the Father,” etc. Indeed, the anger and charges of blasphemy by many of the Jews at Jesus' time show that Jesus’ claim to divinity was far better accomplished this way than to us a more ambiguous term of that time: “Son of God.” 
 
Paradoxically, “Son of Man” is a clearer profession of divine transcendence that can be traced to Daniel 7:13 which Christ appropriated to himself. That prophecy speaks of one, like a Son of Man coming on the clouds to judge the earth, who has a Kingdom that shall never end. 
 
Jesus’ preference for the term is shown when Caiaphas the High Priest said: "I put you on oath by the living God to tell us if you are the Messiah, the Son of God." Jesus answered, “The words are your own. Moreover, I tell you that from this time onward you will see the Son of Man seated at the right hand of the power and coming on the clouds of heaven." (Mt 26:62-66) 
 
Thus, "Son of Man" is a more clear and lofty title, which Christ prefers for himself.