Why would the Speedbrake be required for such a long time on approach? As far as I was aware, the Speedbrake is designed to slow the aircraft down. On landing, I do understand why they are required. Once the aircraft has hit the tarmac, they are deployed to 1) slow the aircraft and 2) prevent the aircraft from bouncing up and down. The airflow over the wing increases doesn’t it? To ‘push’ the aircraft down, as I say, preventing it from jumping up and down. 

I have (7 hours ago) just landed on a B757, but the Speedbrake was up pretty much for 70% of the descent and approach. 




Thinking back to my previous introductory paragraph, the reasoning must have been excessive speed, no? Or a need for the aircraft to slow down dramatically. Is this the case, or am I missing something obvious? 

I know Air France flight 447 considered deploying the Speedbrake when their Airbus gave them faulty warnings of speed and altitude; it was advised then that this would have been completely the wrong thing to do. 

I have never seen it before, as much as I did today on descent, and I wonder why the Speedbrake was required for near on 70% of our approach?
There are two reasons I can think of off the bat: 


Its possible the controller asked them to hold a slow speed due to increased traffic ahead. The brakes may have been deployed to match the speed requested. I have heard this called on occasion over the radio in the terminal area I fly.  
The controller cleared them for a steeper decent than usual this would cause them to potentially deploy the speedbrakes to make the descent rate. 


This article discusses it in reference to small planes but idea is the same. And another article by a CFI here.