The set of themes that comes with Keynote doesn’t include a lot of footer material, but your organization may have so-called design standards that require them. If so, you’ve probably found that in Keynote, you have to update each master slide individually, whereas in Powerpoint, you can generally set the basic text fields of all your slide footers in a single action.
If you build your theme a little differently, though, you can get the same degree of convenience in Keynote.
In my organization’s Keynote template, all the footers are little two-cell tables with a cell for names and a cell for a date. There’s a separate table in each master slide. I changed the contents of all the footer tables except the first one to be the formula
=Title and Content::Table 1::A1
or … B1 for the second cell. “Title and Content” is the name of the first slide master that has a footer. Now I just have to update that one master and all the slides that have footers get the same text.