Toggling Flight mode does not cost an action or end the turn. Movement or elevation changes while in flight costs 1 fuel unit and 1 action.
Fuel cost is unrelated to the number of tiles traversed during a movement. Traveling one tile or the maximum possible in one action consumes both consume one unit of fuel.
Hovering in a stationary position does not consume fuel.
Flying does confer an elevated-position bonus, but the soldier must fly higher than normal, which takes an action.
Using Archangel Armor with a Sniper with the Damn Good Ground ability can make any enemy, even Sectopods, less of a danger. Also, this largely removes the issue of seeking out and securing a "nest" for a Squadsight Sniper - at the cost of one action point and one fuel unit, an unrivaled firing position can often be achieved without leaving the original drop zone.
Has a bug that can cause a flying unit to get stuck in buildings or ship structure, also can occur if the soldier runs out of fuel over an obstacle that normally cannot be walked on. Prevents the wearer from moving, including ceasing to fly, but can still shoot and/or die.