A criminal defendant is obliged to provide a defence response to the crown opening. The response has to touch on each of the paragraphs presented in the crown opening by replying to each of the issues mentioned.
Admissions of the accused on certain facts are made known in the defence response (eg. being at a specific place at a specified date and time). Through this, the scope of the case gets established and the people are informed on the issues that may be raised. The defence may also point out any evidentiary issues when drafting the response (eg. challenging evidence on grounds of confidentiality).
Generally the Court are trying to find out what is going on in responses. They are not helped by a response that does not explicitly explain what the defence is. By this time you should be well aware what your defence is.