For your first question, yes, it can be optionally turned on and set to a specific value. In the early days of Swift it was quite useful. I still have it on in one project but it rarely shows up anymore and when it does it is usually a mystery as to why it shows up and there's no clear way to fix it.

For your second point, this is mostly the case for Swift as well. 123 defaults to Int so if you wanted a floating point you'd have to write let x: Double = 123 or let x = 123.0. Most people will default to the latter because it is less typing.