Similarly to colors you should use the same font styles and sizes across the entire presentation.
That means all slide headings and subheadings all chart and text box headings all numbers and labels
inside charts all side comments all text boxes page numbers and footnotes should follow consistently
the same font pattern on all slides.
Again using the same template slide from the outset would help maintain that standard.
Try to be consistent in terms of both font family and font size.
If you are creating a presentation that is an aerial then your entire presentation should be in areal
text boxes objects charts and other elements all text elements should be in Ariel.
The question regarding font size is a bit more subtle.
You can have text with different sizes however what you should remember is that you have to be consistent
if the text box on your first page has a font size of 12 then the rest of the text boxes in the presentation
should also have a font size of 12.
If the font size of your charts is 10 then all charts should have a font size of 10 and so on.
We are sure you get the point consistency in terms of font style and size is another important step
towards developing professional output.