If you are involved in an 'incident' or god forbid an 'accident' and you are no longer around to tell the tale (or even if you are), the fact that you may not have used correct ATC phraseology could be used to hang the 'PILOT ERROR' tag on you by the Press, the Company you have worked so loyally for or the AAIB.
Nice for the industry, your colleages and your family..
.
Always read back what is said to you
cover your arse and the arses of your crew
