Imagine a page with 50 links, that you each have to download by hand? Nope! Just DTA and a filter to choose what you want.
Photo gallery? Same!
Open a bunch of stuff in different tabs, and want to download the same thing (eg. .zip file) from each open tab... DTA all tabs, and *.zip filter.
Regex filter? Sure!
The basic download manager part is just an extra feature, that you usually don't need.
Should I only use the one provided by my Web browser? Should I not download the content that I want to access locally or share between devices without being obliged to stream/download it again from a server?
If I find a gallery of images that I like to keep. I can use gallery-dl for that and use gallery-dl "instagram.com/boburnham" in the command line and it will crawl and download the images within the gallery.