At least "BLOCKED" is not just confined to the area I'm working in then! It gives me some satisfaction after I've issued an instruction, heard someone say "BLOCKED" only for the original recipient to read it back in full!
Most of the time there's a side tone for us ATCOs anyway which lets us hear when someone else is transmitting at the same time...but some R/T discipline (from both sides) wouldn't go amiss!
-HD-