You don't need to register a namespace before uploading a new module.

As far as I can tell, the only purpose of registering a namespace is to prevent others from uploading modules into subnamespaces (for example PDL::SomeMatrixFunc::ReallyFast). I think it doesn't even prevent uploading, search.cpan.org just shows the "not an official upload" warning in red letters.

I have uploaded about 9 distributions to CPAN, and haven't registered a single namespace for any of them.

The only other reason to register a namespace is to be included in the topic list shown on the search.cpan.org homepage. But that list is barely useable and most people search nowadays and don't bother to browse.

I personally hate reserving without uploading. When I searched CPAN to see if a namespace was in use before I uploaded my own distribution, nothing showed up. But when I uploaded, mine was listed as unauthorized because somebody years ago had pre-registered it and never made use of it. The author also refused a request to assign it to me, claiming he one day plans to make use of it. There are many claimed, but unused namespaces like that.

1: https://pause.perl.org/pause/authenquery?ACTION=peek_perms

Please don't use square brackets in the manner above. If your taste in formatting footnote pointers runs to [...] use &#91;...&#93; because the local variant of HTML uses square brackets the way standard HTML uses <a href=...</a>.

That means you could also have created the link thusly:
&#91;https://pause.perl.org/pause/authenquery?ACTION=peek_perms&#93;
which would display the url, linkified;
or
&#91;https://pause.perl.org/pause/authenquery?ACTION=peek_perms|<super>1</super>1&#93;
which would render as ^1. -- a superscripted 1 -- and thus would serve as a link to PAUSE as well as a pointer to a footnote... probably not what you want, here, but useful in some cases.

References: Perl Monks Approved HTML tags, Markup in the Monastery, What shortcuts can I use for linking to other information?, and Writeup Formatting Tips

You may find the following links useful:

perlnewmod
• Register your namespace!

There's very little reason to register module namespaces these days. Most people don't.

• TOBYINK (me) - 127 distributions; 7 are registered
• RJBS - 255 distributions; 2 are registered
• ADAMK - 245 distributions; none are registered
• STEVAN (of Moose fame) - 73 distributions; none are registered
• FLORA (famously everywhere) - 201 distributions; 6 are registered