I agree with PaulB.

When a flat file is presented, the layout/structure is typically well known. That is part of the initial discovery.

If there are freeform notes or something, I can totally see a reason to make that column in the staging table larger.

In general, best practice is to start bringing the data in using a table definition as close to the final destination table as possible. There will be some tradeoffs depending upon how well you can perform an initial scrub/cleanse from the flat file. But never grab numeric or date data and place it in a varchar without good reason.

I typically use SSIS to import flat files. I always run through the flat file and define it with the proper datatypes up front. This not only makes life easier in subsequent stages, but it lets me know up front if the data structure I was given for the flat file is correct, or even if there is errant data in any of the file's fields.