Quite often there is a need to fetch a new copy of a file only when
the source file to be copied over has changed since the local version was last
updated.
To avoid an unnecessary fetch over http(s) it would be useful to add two new
command line options to fetch.
- One to specify the time to use in the if-modified-since header of the request
directly from the command line.
- Another to specify a reference file whose modify time to use as the content
of the if-modified-since request header.

None of this of course would work for ftp, but for http and https it would be
a major benefit to be able to avoid pointless downloads when the local data
is already as fresh as the data that would be pulled in.
When fetching with http or https over a long distance connection the amount of
time saved could be huge.

Fix: 

The only known fix is to add the if-modified-since header and
ability to parse to the potential "not modified" response.
How-To-Repeat:               Just copy a few large files over a long distance connection using
fetch when your local copy is already as fresh as the one you receive, and you
should instantly understand why I am proposing this.