Projectile speed and attack speed

I made my first ranger yesterday and i was wondering what the point is of projectile speed.
If i understand it right attackspeed is how fast you attack ofcourse and projectile speed is how fast your arrows fly? But whats the point of faster flying arrows if it doesnt make you attack faster?
Only thing i can think of it when you shoot on moving mobs you want your projectiles to hit the target faster? not sure what to think of it. I hope someone can fill me in about this.

on skills like Ethereal Knives, Freezing Pulse or Spectral Throw projectile speed would increase the travel distance and so the range. so you can hit monsters further away from you.

Projectile speed also increase some skill attack range. Like: EK, Spectral Throw, Freezing Pulse and so on. It also decrease Rain of Arrows flying time.

Faster projectile support gem also increase projectile damage + quality bonus.
http://pathofexile.gamepedia.com/Faster_Projectiles

When it comes to simple bow skills you aren't going to see a big different in all situations since arrows travel at a relatively fast rate. If you're standing still and something is heading towards you faster projectiles aren't going to matter much.

But you could imagine a scenarios where it could matter. A rare necro with haste aura is running away from you, heading down a hallway and if he gets away he'll be in a room full dead skeletons you just killed. Your arrow flying at a faster speed could make the difference between killing the necro before it turns the corner rather than him getting away. Or perhaps you're shooting at a pack of flicker spiders, faster arrows might be able to hit before they teleport.

As other posters have said, there are tons of other skills that also have projectile components where the support gem can make a big difference.