Some questions about using CComPtr (when use Release()? Can I return CComPtr?, ...)

I writing add-on for Internet Explorer(BHO) and I'm using CComPtr smart pointers. I wonder:

1. When should I use CComPtr.Release() function?

In this this link it's used to release browser object. Where else should I use it? In 'normal' use (with my own classes) I don't need it. Should I use it in this situation:
I get document object using m_spWebBrowser->get_Document(&spDispDoc):

void STDMETHODCALLTYPE CHelloWorldBHO::OnDocumentComplete(IDispatch *pDisp, VARIANT *pvarURL)
{
    // Query for the IWebBrowser2 interface.
    CComQIPtr spTempWebBrowser = pDisp;

    // Is this event associated with the top-level browser?
    if (spTempWebBrowser && m_spWebBrowser &&
        m_spWebBrowser.IsEqualObject(spTempWebBrowser))
    {
        // Get the current document object from browser...
        CComPtr spDispDoc;
        hr = m_spWebBrowser->get_Document(&spDispDoc);
        if (SUCCEEDED(hr))
        {
            // ...and query for an HTML document.
            CComQIPtr htmlDoc2 = spDispDoc;
            m_spHTMLDocument = spHTMLDoc;
        }
    }

}

Should I release spHTMLDocument in SetSite function like I do with m_spWebBrowser (like in link mentioned before)?
2. Can I return CComPtr from a function safely?
I mean like this:

CComPtr getObjects(CComQIPtr<IHTMLDocument3> htmlDoc3)
{
 CComPtr objects;
 hr = htmlDoc3->getElementsByTagName(CComBSTR(L"object"), &objects);
 if(SUCCEEDED(hr) && objects != NULL)
 {
  return objects;
 }
 return NULL;
}

3. Should I never use normal pointer?
In previous link RemoveImages private function is declared this way:

void RemoveImages(IHTMLDocument2 *pDocument); 

but invoked with smart pointer:

CComQIPtr<IHTMLDocument2> spHTMLDoc = spDispDoc;
if (spHTMLDoc != NULL)
{
 // Finally, remove the images.
 RemoveImages(spHTMLDo