For example, I might want to allow 3rd party cookies on a work profile but not on a personal profile.
The personal profile use my personal mail, and has various container tabs as needed.
The scouts profile use the scouts email for syncing, share with my fellow scouts.
The fencing association I manage syncs with my personal email in the association's domain, and it has 3 containers: association-personal (for my files and email in google workplace), association-admin (for managing the whole workplace) and backup (recovery email for the workplace and for some other external services before workplace).
With containers only the sync will not work, and also I will be nagged to "switch to this container" everytime I open a google-related page, which I use with 5 different accounts. Profiles and containers fit perfectly my use case.