You do not need to have a physical address when creating an event, it is not a required field. The Benchmark Events tool however does include a mapping feature that automatically displays the address on a map, this can be disabled if your venue or address is not real or physical. However what is required is an event host and email address as a form of contact.
If you want to send an invitation with Benchmark or commercially send an email at all, you must include a physical mailing address. This is pursuant to the CAN-SPAM Act 2003 which requires that all commerical/bulk email to contain a physical mailing address. Benchmark will not allow emails to be sent without a physical email.