[mjs]

This seems to run whatever code usually runs when you hit [space] on a filename in a Finder window. (Except that it outputs a bunch of debugging information.) Under what circumstances is that any better or more useful than "open"?

[micampe]

Correct (man 1 qlmanage). Depending on the type of file, it is usually faster to open quicklook than opening the file in its default application, especially if you just want to take a look and you don’t actually need to edit the file.

[cooper12]

You can hide the debugging info by redirecting the output streams.

    $ qlmanage -p <file> &>/dev/null

[lexy0202]

Because it essentially acts like quick look for the terminal.