The travel speed is how fast your printer's hot end moves through an open space between sections of your model for each layer. For example, the amount of time it takes for the hot end to transverse between the two columns and dome might allow enough time for your hot end to ooze a minimal amount of material. This excess extrusion will transfer to the next section of the model, creating an unwanted buildup.
You'll need to test the model made with SketchUp. If you would rather download the model, it's available at http://www.thingiverse.com/thing:152695. This recipe is also better illustrated if the PLA filament is used.
We will proceed as follows: