Little Disk Space - Gnus Manual

The startup files can get rather large, so you may want to cut their sizes a bit if you are running out of space.

gnus-save-newsrc-file: If this is nil, Gnus will never save .newsrc—it will only save .newsrc.eld. This means that you will not be able to use any other newsreaders than Gnus. This variable is t by default.
gnus-read-newsrc-file: If this is nil, Gnus will never read .newsrc—it will only read .newsrc.eld. This means that you will not be able to use any other newsreaders than Gnus. This variable is t by default.
gnus-save-killed-list: If this is nil, Gnus will not save the list of dead groups. You should also set gnus-check-new-newsgroups to ask-server and gnus-check-bogus-newsgroups to nil if you set this variable to nil. This variable is t by default.