IMO, as long as you read/write only thorugh your ASP application, it is not harm setting read/write permissions for those folders. Actually that is set only for the IUSR_yourMachine account, and that does no harm.
But you should be sure that you separate the folders that you use for creating text/pdf files from your other folders, so that permission is set only to these folders, not to the entire web app folder.
Hope that helps.
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