[Closed] Double spacing after a full stop?

My wife says this is standard practice and the correct way to do things, yet I've failed to find any evidence of this in any correspondence from any company currently in my home.

A little research on the internet reveals that she's right, but it's now seen as old fashioned and that it's rarely seen any more with modern fonts and word processors. Double spacing can also be seen as 'gappy' and distracting from the message you're trying to convey. Your thoughts?