conditionals - What does the expression "If + subject + was/were + infinitive" mean in American English

I just want to ask you guys about the general meaning of expressions that use the following pattern in colloquial American English:

If + subject + was/were + infinitive, ...

Examples: (Written by native American Speakers)

1. If I was to make a booking, which rooms are the closest to the pool?


2. If I was to say what I am, I'd be a Labor man.


3. If you were to buy the iPhone 8 plus, will you be able to get it activated through Boost?


4. What would happen to a cactus if it was to be planted in a rainforest?

And here is what I think it means: It’s a way to express a condition that didn't happen, and it could also be used to express a condition that is likely to happen in the future as in the first example.

Is that right, do Americans use the expression often?

Please, correct me if I'm wrong.