These are not the type of volunteers that come do your work for you.
These are plants that return from the year before.
Maybe from going to seed or being accidentally left in the garden.
Below are two examples from plants that were allowed to go to seed last season.
The Borage will probably be moved closer to the zucchini plants, as it is beneficial to squash.
Beneficial flowers will often go to seed and come back up the next year.
Cilantro also re-seeds well. Cilantro seed is Coriander.
I often have Volunteer Potatoes that come up from the year before.
It is still to early in the season for them this year.