In desktop logos we've 3 type of variations. Default logo which is common, and retina logo is called only for retina display devices like iPad Retina, iPhone Retinas. Then, WordPress admin logo will only get affect in your login page of WordPress admin, which is like : http://yoursite.com/wp-login.php

• 1

  Default Logo

  Default logo is basic type of logo. Which will call in every header and every devices. So, first and foremost important logo format is default logo. But if you loss image quality in retina devices, you've to upload retina logos too.
• 2

  Retina Logo

  Retina logo is only for retina devices. So, please upload 2x size from your default logo. You can also control this large logo width and height from our theme options. So, you'll not loss logo image quality in retina devices.
• 3

  Transparent Header Logo

  This header option will find under page options. Each page metabox you'll find header transparent option. That'll make header as transparent look. So, some of brand logos will not fit transparent background colors. In that time you take advantage of this feature.
• 4

  WordPress Admin Logo

  This is just a login page logo of your site admin. There is no more trick on it. If you not upload any logo in this area, you'll get default WordPress logo as it is. Login link will be like : http://yoursite.com/wp-login.php

In mobile our menu structure will change, and it's only focused for menu bar. In that situation your logo may look different because of menu design structure change. So, you can utilize this option in that situation. There you'll see only one logo upload field. Due to only for mobile, upload retina logo in that location. Also, you can have same option of logo width and height. Top and bottom spaces.