When to Wordmark?

There are, of course, good reasons to create a symbol as part of an identity program. For example, if you have a long name, like in the case of The Chase Manhattan Bank (now simply “Chase”), a symbol may help tie it together as a unit and add visual impact.
Or, a symbol can help link together many divisions or branches under a single institutional identity—as in the case of the Smithsonian Institution.

But absent a good reason for a symbol, it is always a better idea to start with putting the emphasis on the name and trying to find a simple, focused way—a change of color, an unusual arrangement of letters, a graphic accent or even just a unique lettering style—to make it memorable.
An early example of this approach is the wordmark Tom Geismar designed with the red O for Mobil Oil exactly 50 years ago.

http://www.printmag.com/branding/when-to-wordmark-2/