Why would I want this?

Because you like having the latest syntax highlighing for every language, but don't want to manually install (and keep up with) which is the latest for each language. Note this is pure syntax highlighting, and bulky language packages (like Markdown All in one, Julia Language Support, Latex Workshop, etc) are not included.

Do I need to enable this?

Changes should be applied automatically as soon as you install.

Created Your Own Syntax (or know of a better one)?

Complain on here! (make a new issue) and I'll add/update the extension.