I have discovered how useful Data fields are in terms of working process, have I sent info to this person or not.
We use them to easily create a workflow.

We would be able to add the same value to multiple selected people, just as it works with tags, to the data fields. And that without importing via CSV-file.

As for now we have to open every single contact, to add the same value.
To do this with tags we would end up with way too many tags to provide the workflow we want.