How Does the Drupal 8 Media System Simplify File and Image Management?

https://www.drupal.org/docs/8/core/modules/media

In Drupal 8 we use a new system called Media. This system is a very bare bones "Document Management System" or Asset management system. Instead of how older systems allowed you to FTP or place / upload files to any directory you like, this requires you store them through the add/edit file or media options in Drupal. 

It is our goal, although not always the case to store all files, images, and documents into the media system of Drupal moving forward to give you a reusable and updatable file system, where updating files is simple and direct.

Drupal itself has different operations for files, images, and other file storage types but almost always stores these files under /sites/default/files/[filename] or in subdirectories.

Media management allows for multiple media types. Some media types should be segmented to allow for rules or segmentation of type. For example slideshow images are a large wide format which is very specific. It would make sense that these files would have different requirements, and probably not be used in non-slideshow areas. A media type just for these and configuration of directory could be setup to have a filterable list of just slideshows for creating content. 

Within media, it's reusable and globally updatable so if you update or overwrite one media item, it will update it globally.

Images don't specifically require you to upload at certain sizes, and the imagecache system will implement specific sizes for the areas it's displayed on the site. It is important however to keep in mind the final output size while uploading and choosing the right frame for your image. Rectangle, square, circle, or portrait. It's important to choose the right layout for your uploaded image.