Please forgive me if this is a naive question !

I have about 420k miles with CO and am Platinum elite. I've never redeemed any miles for any type of award. Reading through many of the posts here, there are many comments on how useless the miles with OnePass are.

What can I use these miles for ? Looking at all the award charts on the CO website, I assumed that I could use these to fly from UK to the US and other locations...is this not true ?

What sort of restrictions/issues could I expect if I wanted to use such miles ( I understand about blackout dates)

TIA