Roger S - maybe you should consider the case when one would like to stay at ones cruising level for more than the one minute permitted by the AIP after an instruction to climb or descend.
That's when it is important to confirm the "when ready" aspect.
Now for my own personal gripe - people who say "ABC maintains FLXXX". I believe it has something to do with an incorrect form of the verb "to maintain". Ditto for "ABC descends FLXXX" and "climbs".
Why can't people just stick to what's in the book (ie "maintaining", "descending" or "climbing") rather than trying to invent their own radio techniques? Now that was a rhetorical question, but I expect some here will take it literally.