It was never useful for IMAP, and NNTP hasn't needed it since:
1bf653ad139bf7bb (nntp+www: drop List-* and Archived-At headers, 2020-12-10)
PublicInbox::IMAP::ensure_slices_exist($imapd, $ibx);
# preload to avoid fragmentation:
$ibx->description;
- $ibx->base_url;
# ensure dummies are selectable:
do {
$dummies->{$ngname} = $dummy;
# only valid if msgmap and over works
# preload to avoid fragmentation:
$ibx->description;
- $ibx->base_url;
} else {
delete $groups->{$ngname};
# Note: don't be tempted to delete more for memory