Double spacing after end of sentence punctuation and colons went out with the advent of computers and non-monotype. Double spacing is still appropriate when using monotype fonts, however, such as Courier New. That said, I have a hard time breaking my double spacing habits because I learned to type on IBM selectric and continued using these machines during my time as a legal assistant. This was many years ago, but I have a hard time with old habits that are so engrained. When is or was triple spacing ever appropriate? I've never used it.