Hi Priyanka,

Design templates is used to capture your application design in premade templates.

Advantages:

• Codify design patterns in your application
  
  • Ensures consistency of layouts
  • Easy to reuse these patterns elsewhere
  • Provides common language between designers and developers

• Updates to templates will be reflected immediately in any instance that uses them
• Make template instances editable in Express

You can get more information from the below URL:

https://community.pega.com/sites/default/files/help_v74/procomhelpmain.htm#ui/ui-design-templates/ui-design-templates-con.htm

Thanks!