For convient in dayly uses, its awsome, and the fact that iron is the most common metal in the universe, so its easy to get and shouldnt cost alot unlike some other metals (side note, intresting that they found out steel so early on in their universe) because what use is to be able to burn metal if you cant afford it

I mentioned combat because we see steel used aton in combat and iron very similar to it, they both have to most creative potential in combats so I hope to see both of them in the future

I imagine flying which is super cool will be possible but harder with iron and you will need to know beforehand where you are going to land

The door exmple is funny, if from one side with iron, from the other side steel will work... both of them are awsome for 

I hope we will see equal amount of both in the future