A Common Experience
However an audience member feels about the speaker and their topics, the speech gives everyone the same experience in the room, making for an easy conversation topic to bond over afterwards. This is especially valuable when you have multiple departments in the same space who likely don't interact very often.
Inspiration In Unlikely Places
Keynote speakers are used to trying to rally a crowd, but the speaker may be able to go a step further by motivating the group. When a Huffington Post study shows that less than half of Aussies like their jobs, this could be one step toward infusing some vigor in the employees. Plus, it shows that you're engaged enough to invest in your employee's well being.
Reinforces Your Message
Sometimes employees may be told information over and over again, without ever really understanding it. Keynote speakers give you a fresh way to state a company mission, or just review some of the general principles you've been trying to instill. Your employees may feel more confident in what they do once they have a clearer picture of the path forward.