1. A computer-implemented method for classifying files as candidates for deduplication, at least a portion of the method being performed by a computing device comprising at least one processor, the method comprising: identifying at least a portion of a file; detecting an event that is suggestive of a duplicate instance of the portion of the file already being stored within a storage device prior to determining whether the duplicate instance of the portion of the file is already stored within the storage device; in response to detecting the event, classifying the file as a candidate for deduplication such that the file's candidate-for-deduplication classification indicates that the duplicate instance of the portion of the file is likely already stored within the storage device; maintaining the file's candidate-for-deduplication classification for use in prompting a determination on whether the duplicate instance of the portion of the file is already stored within the storage device by maintaining an attribute associated with the file that indicates that the file is a candidate for deduplication; reducing the amount of time or resources needed to determine whether a set of files that includes the file qualify for deduplication by, during deduplication or backup of data within a storage system: identifying the attribute associated with the file; determining, based on the attribute associated with the file, that the file is a candidate for deduplication; in response to determining that the file is a candidate for deduplication, determining whether the portion of the file is already stored within the storage device.