Obviously the physical talk of upwards travel to a place beyond the observable world of earth-and-space both assumes and contributes to an understanding that "heaven" is above us.
It also offers a physical image to match the increase in glory and honour implicit in the idea that Jesus is now 'exalted' to the right hand of God (i.e. seated on a throne on the right side of the divine throne).
With exaltation the victory won in the resurrection, the defeat of the power of death as the last enemy against humanity is completed.
With departure the door is open to a new history of God being present among God's people, God the Holy Spirit will dwell among them.
We misunderstand Ascension and its importance if we think of it as (say) a postscript to the life of Jesus, or a snapshot of the glory of the exalted Jesus.
Ascension is also the beginning of a new era in our history, the time when we are responsible for the continuation of the mission of Jesus Christ.
Luke in both texts is keenly alert to this point. If (as some scholars of Luke's writings have supposed) Jesus has come in the middle of history, then we are now in its last period. That this is so, according to Luke, is underlined in Acts 1:11. Jesus has departed, but he will return.
There is a sermon in every verse of this passage!