When building a Campaign, when you choose to have an additional donations as an option, it changes the checkout process and requires the registrant's address even if they do not choose to to donate. This has caused confusion for some registrants with the extra steps as many of our events are free but have additional donation as an option.
It would be much more ideal for the additional donation and the registrant info field to be on the same page, then have them enter more complete info if they need to enter payment info.