the font is used for the sorting and pagination arrow images. Please see https://tablepress.org/release-announcement-tablepress-0-9-rc/ for more information.
Basically, this is not a font with regular letters, but a font with icons or images. This has the advantage that the browser does not have to load (at least) five different images files in five different HTTP requests, that the images/arrows will look sharp in all sizes and resolutions (for example on regular and on retina displays), and that font attributes, like color or shadows can easily be changed or applied.
I understand that there are plugins that search for "base64", but I these are indeed false errors in this case. Not everything that can be done with "base64" is bad or evil, as this demonstrates.
So, the icon font (and with that the inclusion of the font into the CSS file via "base64") is here to stay, due to all the advantages it brings.