Entering multiple values into a metadata field that supports this is pretty tedious:
Click on the field to make it editable
Enter your value, which might include copying and pasting an individual value from a different list, which might be formatted in such a way to make this very hard
Accept the value somehow (press enter or leave the input field)
If you have the list you want to put in a field already at hand for copy pasting, it might be useful to be able to just copy and paste it in bulk.
The idea here is that the data you put in a given field will probably mostly come from the same source. So let's say you always have to enter the contributors from a text file which has them as a comma-separated list. It would be cool to be able to somewhere configure the contributors field to accept lists separated by comma. If you then paste a string with this delimiter into the input field, the admin UI should automatically split (and probably trim) it upon accepting the value.