Import has multiple options. such Live import and Queue import
In live import, you can see the import in from of you and you have to wait till the very end until your complete contact list won't be imported, it may take some time based on how big your list is.
In the queue import, you can you do not need to wait for the completing of your complete list.
So when you will upload your list with queue import option then the complete list will be uploaded on the server directly and will be imported into your contact list in some time based on your list size and number of the contact.
But the benefit is that you do not have to wait for it and switch to another tab, maybe create your email template or create your email campaign till that time instead of waiting.
The queue is a much faster option compared to the Live import also it will minimize the interrupts between your import due to any time-out.