Theoretically, Yes companies merge to achieve value-adding...

Theoretically, Yes companies merge to achieve value-adding synergies. Most of this is from economies of scale, goodwill, tax benefits, market share etc (as you mentioned). However, how often does theoretical translate into actual performance? Vocus has stated that synergies are proving to be harder to achieve than anticipated and they are having to spend cash, increase costs, to integrate systems at the backend. M2 and Vocus operated on different systems/platforms and this is causing issues for them. They were struggling in the corporate space due to these issues. They have also written down some goodwill and are relatively flat on the growth side. So when we look at actual performance, the merger has yet to yield the results of market expectations. This is why the stock has suffered a battering. I think it will be at least 18 months before we see some good uplift in synergies, if at all. This is not to say that the share won't appreciate in the short term as markets can be irrational but the benefits of synergies are definitely further down the road.