The purpose is to check for any inconsistency fonts used across the web application so that the developers can fix the issue.
Consistency in terms of all font properties (Font families,font sizes etc.) needs to be checked. As suggested by Pekka below, I can use CSS to define consistent font properties which can be used in all web pages but how can a QA auto test this and confirm the same CSS and hence the same font is applied to the entire web application?