Why do passengers need to pull up their window shutters when planes are taking off and landing?

Why do passengers need to pull up their window shutters when planes are taking off and landing?

Not necessarily, on some afternoon transcon flights on Virgin America they had the window shades pulled the whole way. It was strange because I didn't know when the plane was going to hit the tarmack. However, it did make the mood lighting look impressive!

In case of a crash situation it allows emergency services to see what's happening (or not)  inside the cabin. 

It is to assist in the event of an emergency.  Crew need to be able to see out the window to see if there could be any hazards, such as fire or any other obstacles.. electricity wires etc..

Like Koru17, my experience of flying domestic in the US is that no one cares if your shades are down, so I assume this regulation differs between countries/airlines. 

Apart form letting people look into/look out of the plane, lifting the shades also helps your eyes adjust to the natural light before landing in case there is a need to evacuate. This is also why the lights in the plane are swicthed off before landing. It's important beacuse survival rates for emergency evacuations decreasce dramatically after 90 seconds(it's why 90 seconds is the maximum time for a full evacuation in aircraft safety testing), so not wasting time adjusting to a suddenly bright/dark enviroment just so you can find your way to the exit can save lives.