Hi Nanette,
The impact of ignoring fields is not having to manually remove extraneous columns from your data file before you can import! It is very common that source systems output data that are not needed, or are not desired, or have nowhere to go, in Raiser's Edge.
Being able to simply ignore those columns saves time, and reduces your margin for error, when compared to manually manipulating the data files each time. As Erin mentions, the ignore feature makes it easy to use those columns, in the future, should they someday contain data you wish to import.
Thanks!
Tiffany
Nanette Klimkow