When pulling a gift or gift summery field into an export, RE allows you to set the criteria of the gift types to export or summarize. By default it excludes Write Off gifts. User or Supervisor should be able to set a default for the types of gifts that are exported.
For example, we don't ever count pledge amounts in giving totals. I want that gift type to default out of the gifts included in a donor gift summary total.
So create your donor gift summary and use that as your Master / Default summary with the gift types you want and change the fund/dates etc.
I would not want defaults set as different users would need/expect different things - to me better to choose what you want per case.