You need to train the users to NOT manually overwrite fields. And, some clients don't want fields. Very little time savings if you are working on drawings already created, or if project information changes infrequently.
Oh, really big disadvantage: a sheet can only belong to one sheet set. So if you want to automatically include the same logical drawing in a sheet set you need to either copy the file or do some serious juggling.
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If you are going to fly by the seat of your pants, expect friction burns.