Tab leaders are used on menus, price lists, and contents pages. Their purpose is to guide the eye from one piece of text to the next. There are other solutions, arguably preferable, that don't introduce gaping holes between the item and its page number or price, but so long as the distance between the text and the number isn't too wide, this can be a good solution.
Figure 12.4. This menu uses a right tab with leader characters (a period followed by a space) to separate the menu item and its price.