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Not OP but read about it on this hosts config [0].

From that page:

> We prefer to use 0.0.0.0, which is defined as a non-routable meta-address used to designate an invalid, unknown, or non applicable target.

> Using 0.0.0.0 is empirically faster, possibly because there's no wait for a timeout resolution. It also does not interfere with a web server that may be running on the local PC.

[0] https://github.com/StevenBlack/hosts

For 127.0.0.1 it will try to connect and fail, either right away or on timeout depending on the on-box firewall setup.

For 0.0.0.0 it won't even try to connect (or fail instantly depending on how you look at it).

I usually have a web server running on posts 80 and 443 on my local machine. Using 127.0.0.1 will make requests to Facebook end up there, which is not necessarily what you want.