This is a reoccurring question I see from time to time.
The short answer is NO. Not everybody will have a smart phone with scanning possibilities is the obvious reason. In my opinion a QR Code should not link to the same (base/home) url as placed on a advertizement poster.
If your company is called "abc" and your website is www.abc.com, why should you place a QR Code on an advertizement linking to your abc homepage? There is hardly any added value linking to this page using a QR Code.
But if in your advertizing you promote product "xyz", and the link to this product page is something like:
"http://www.abc.com/products/mobile/specs/xyz" a QR Code to link to this product page is a good idea.
Even a shortened link to this page like "http://goo.gl/AbCdE" is better replaced by a QR Code.
Another example is a QR Code to a social media page, since a QR Code replaces a relative long link.
In both examples the QR Code should be accompanied with an instruction. "Scan for more info" or "Like Us on Facebook" could be the basic instructions for the mentioned examples.
Also make use of a Custom QR Code, so the threshold to pick up the phone and start scanning the code is even lowered even more.
Should you require such a customized QR Code, please visit my site to see examples of what is possible with QR Codes. Doesn't the site show what you are looking for, don't hesitate to contact me to discuss your specific needs.