The good thing about standards is everyone understands it. Must admit I've had some nationalities comming through that honestly didn't understand what I was trying to tell them/ask them about (some nonstandard about openings and so on), but when it came to the normal "taxi, climb, turn...." and so forth, everything went smooth.
So yes, knowing your standard phraseology really helps a lot, and the better we all are at it, the less risk for misunderstandings
And if you really want to go at it, with americans and englishmen alike doesn't need to learn it, cause it's their native tongue, remember how the community is about french, italian, spanish and all the other national languages.... Speaking on the frequency without using the ICAO standard phraseology is comparable to using said languages, some actually doesn't understand you, and it hurts safety