For example, we use Podio as the company's main CRM, they have a Unique ID for all the contacts, itd be nice to have any CSV pushes/Webhook updates use the custom field to merge/update.

Now, let's say I import that same lead later on when I have their email.

This would not map to the contact, so it would therefore create a duplicate.

But, if I could have set the linkedin URL field as a unique identifier, I wouldn't have this problem!