Among other things, the right to retain and instruct counsel under section 10 (b) of the Charter obliges police to “‘hold off’ from attempting to elicit incriminatory evidence from the detainee until he or she has had a reasonable opportunity to reach counsel.
R. v. Prosper,  3 S.C.R. 236, at p. 269.
This helps ensure that detainees understand their legal rights and obligations, and most importantly, that they understand their right to remain silent, so they can make an informed decision about whether to waive their right to silence after receiving legal advice relevant to their situation.
The standard police caution, customarily read to the accused upon arrest, informs the suspect in plain language of his/her right to remain silent.
For instance, it may be as brief as:
“You are not obliged to say anything but whatever you do say may be given in evidence. Do you understand?”
The question, “Do you wish to say anything in answer to the charge?” has also been a common feature of the standard police caution.
See for instance R. v. Singh, 2007 SCC 48 (CanLII), at para. 31.
While a police caution is not mandatory, courts quickly recognized that the presence of a caution helps prove that a suspect made a voluntary statement.
R v Boudreau, 1949 CanLII 26 (SCC),  SCR 262, 7 CR 427;
R v KF, 2010 NSCA 45 (CanLII) at paras 21-38, 290 NSR (2d) 387.
Where the accused has invoked his right to counsel, the question, “Do you wish to say anything?” violates the constitutional duty of police to hold off under section 10(b) of the Charter if that question elicits an incriminatory response from the accused.
R. v. G.T.D., 2018 SCC 7.
Postscript: If you have enjoyed this blog, please keep an eye out for upcoming publications from me in 2018/19.