My understanding was that even admins should tag, if
there's anything
there that's at all subjective (anything much above
page-blanked-by-author, random text, whatever). It certainly seems
more sensible that way.
(I usually try to, but...)
[[WP:CSD]]:
"The "Speedy deletion" policy governs limited cases where Wikipedia
administrators may delete Wikipedia pages or media "on sight" without
further debate. Non-admins can request deletion of such a page by
adding an appropriate template (see below). The word "speedy" in this
context refers to the simple decision-making process, not the length
of time since the article was created."
I interpret that as admins being able to delete without tagging. The
whole point of CSD is that it's for uncontroversial deletions. If
there is anything significantly subjective about it, it should go
through PROD or AfD.