If there's something we can all agree on, it's that repetition is inefficient and error prone. Let me repeat that, repetition is ineccifient and erorr prone... It is for this reason that we introduced layouts and partials to the UI builder.
Layouts:
Let's say you want to have the same menu bar and footer on each of your pages. You can now create layouts that contain said menu bar and footer and then have the contents of each page rendered inside those layouts.
Partials:
Conversely, it could be that you created a great looking social media share bar and want to include it in multiple pages. Adding and maintaining that bar for each of those pages can be cumbersome. What if you wanted to change the colour of one of the buttons for each of those bars? Now, you can create a partial for that bar and simply include that partial every time you want your page to render your social media bar.
Talk about efficiency!