I am using AutoLayout and Size classes, but with release of iOS10 and new Xcode 8.0, there is one new option
Vary for Traits
varying 14 compact width devices
varying 18 compact width devices
varying 11 compact width regular height devices
This is just an extension as to how to use "Vary Traits" quickly in your project for adding different layouts in iPad and iPhones.
For example, you need a button having different widths in iPhone and iPad, then it can be easily done and viewed at the same time rather than the earlier Size classes wherein for checking each layout , we had to open the preview and select devices.
I have added a button with fixed width 50.
Now if we want to change the size for iPad, then click on the button in the bottom-right corner "Vary for Traits". Now you are good to go with selecting landscape or portrait orientations as per need. Also select height & width tickboxes.
I am now changing the width constant to 400.
Then as a confirmation, we need to click on "Done varying" button. After which the screen looks like
Now when you go back to any of the iPhone devices, the width constraint will be the same as earlier set in iPhone device.