Generating a grouped feed is quite expensive–expensive enough to cause timeouts--and should be avoided if possible. In particular, when a lane has no sublanes, it is  pointless to try to generate a grouped feed. But it sometimes makes sense to link to the 'grouped feed' for a lane without having to check whether or not it currently has sublanes.

For an example, see https://circulation.librarysimplified.org/CLASSICS/, which links to https:/circulation.librarysimplified.org/CLASSICS/groups/1832 and https:/circulation.librarysimplified.org/CLASSICS/groups/1831 as the two options in an age gate. One of these is a real grouped feed; the other is not.