gnus-save-killed-list

gnus-save-killed-list is a variable defined in `gnus-start.el'.
Its value is

t

Documentation:
*If non-nil, save the list of killed groups to the startup file.
If you set this variable to nil, you'll save both time (when starting
and quitting) and space (both memory and disk), but it will also mean
that Gnus has no record of which groups are new and which are old, so
the automatic new newsgroups subscription methods become meaningless.

You should always set `gnus-check-new-newsgroups' to `ask-server' or
nil if you set this variable to nil.

This variable can also be a regexp. In that case, all groups that do
not match this regexp will be removed before saving the list.

You can customize this variable.