To call someone an empty suit implies that you think they are a complete waste of time. Editorials on politicians love to use the term empty suit to describe people seeking presidential office. This or that politician is just “an empty suit,” to quote the words of numerous political critics, and is thus undeserving of our attention.
Some politicians do deserve the title. A senator with a very poor voting record, or failure to attend senate sessions could clearly be called an empty suit because he is not really performing the job for which he was elected. On the other hand, some politicians may advertise themselves as “not just an empty suit” in order to distinguish themselves from their implied empty suit peers.