What a group can define up front
A group defines the batch title, batch description, item count, personal-or-team scope, starting visibility, optional immediate activation, and the shared defaults for item title, item description, status message, and external link.
That is why the group form is best for campaigns, classroom kits, club drops, event giveaways, or any other situation where several items should begin from the same baseline. Public groups also get their own /trackable-group/{publicCode} page when the whole release needs one public-safe landing page.
What a group does not replace
A group does not turn several trackables into one record. Each item still has its own codes, its own route history, its own ownership state, and its own future edits after activation.
A journey can include simple location reports and fuller location notes. Both move the route forward, but the route history stays tied to the saved stop while current visible location notes are rediscovered from the same coordinate.
If an item later needs its own story, images, or different public link, that should happen on the individual trackable instead of trying to force every item in the batch to stay identical forever. The same rule applies if the item ever needs to move to a different group later: remove it first, then associate it to the next group through the supported handoff flow.