It depends. We worked with a 10 day radio-a-thon where donors would make additional donations throughout the 10 day period. Because we always wanted the most recent new constituets for matching we ran new exports often.
We have worked with some of the largest Raiser’s Edge databases out there. A million constituent record export takes some time to process, but knowing how the process works you can always use Query to simply Append the export used for matching. A simple query could be Constituent “Date Added” > a specific Date.
But for the majority of our clients re-exporting a new matching file is not an issue.