Sometimes data from a system could exist in 2 different places. For example Encompass requires a purchase date for memberships. However depending on the membership, this could be the renewal date or the purchase date. This is because a user can pay all upfront, or yearly.
So it would be nice to have the options to say "If field A equals X then use field B", where X could be blank or a specific value. Of course the fields would have to match syntactically for this to work. So Dates could only compare with dates, strings with strings etc.
Another spin on this would be updating the "Transformation" section to allow for mapping fields in the "What will be written to" section