Boarding passages

A question that always assaults me his 'why do people queue up when boarding?'.

We all have our seats assigned, we are all going to board the same plane, leave at the same time and land at the same time. I do no understand the rush.

If you have a small child or children with you, I sort of see the point, the plain his not packed with people on the corridor yet, so you have a bit more of space to seat all your children calmly and answer to all their requests (water, games, books, ipads, food, etc.).

But if you are a grown adult with full command over your sights, than why would you stand in a line for half an hour or more for no benefit at all?

As I am right now waiting to board my flight, there are very little people that stay out of the line and just chill on the waiting area.

Boarding has started, but I don't see the point in rushing. 

Pear preasure?