What is about:blank for?
It is simply a blank page built into some browsers. Some people just like to have a blank page and not have to see/load anything else when they start their browser or open a new page.
The about URI scheme is designated for internal browser use. It originated in Netscape Navigator, the browser that gave rise to Mozilla Firefox. This includes about:blank.
Per IETF RFC 6694, about:blank is reserved for a blank page. Essentially every browser that supports about implements about:blank and it is pretty much the same everywhere.
Because about:blank is little more than a blank internal page, it doesn't depend on any external resources and serves as a good default on metered connections or slow systems.
about:blank is the most fast and clean way to open a browser.
You do not use up your bandwidth, nor wait for a page to download, and you will (presumably [see below]) not execute any code hidden in any page.
"about:blank"
This document defines one well-known token: "blank". The "about:blank" URI refers to a resource represented in the browser by a blank page. [1]
However, even the most elegant and apparently clean pages can hide hidden code (but not necessarily malicious code): for example, go to Google and look for :-) in the code.
References
- The rfc6694 all about the about by the Internet Engineering Task Force (IETF).