Fully agreed, but often these can be solved by reviewing the overall (business) problem. E.g. maybe it's hard / not worth it to process a file in parallel, but

Fully agreed, but often these can be solved by reviewing the overall (business) problem. E.g. maybe it's hard / not worth it to process a file in parallel, but maybe the most frequent use case needs to process more than one file and files can be processed in parallel with much less work.