The Users > Contacts Overview > Import contacts via csv tool is very helpful. 

One thing I’d like to see added to this functionality is matching email addresses to existing users in community and showing that in the invite status. 

If someone on the import list is already in the community, I’d love for that to show in the Invite status (in Contacts Overview) so that I don’t invite them again. This would also allow us to monitor the “close rate” 

Also, upon the import, it’d be good to recognize those users and filter them out of the invite list. The tool already does something similar, it recognized 4 contact records with the same email as just 1 contact.