Why Does Bigin Limit Field Mapping in Google Sync?

Why Does Bigin Limit Field Mapping in Google Sync?

There are three areas where Bigin doesn't allow field mapping in Google: Email, Mobile, and Street Address. You can ONLY map the Google fields labeled Work Email, Work Mobile, and Work Street Address. Why?

Many of my Google Contacts are vendors and business partners who have Work numbers, but many are clients and customers who have their info under Home, Personal, etc. What's going to happen to these clients when I initiate the two-way sync? Will I have to go into Google Contacts and "correct" all the contacts with mismatched fields before syncing? 

Please advise, thanks