AXI write response

I have been recently reading the AXI specification and have some questions about transaction responses.

1.  In A4.3, it mentions that Transactions on the write channels have one or more write responses. How should I determine the number of responses?

2. BRESP is an optional signal, does this mean the manager can ignore this signal or the subordinate can choose not to send a response?

3. BCOMP is used in the case of multiple responses, what is its function?