I write for a living and when you get 10,000 words into a subject it is pretty easy for things to start repeating (phrases and sentence starts), and when you are trying to write convincingly, loaded words and phrases tend to repeat (“clearly” “without question”). These things lower the quality of the writing and turn off readers – even subconsciously, we don’t like bad writing.
How about a super word counter, that in addition to counting the standard pages/words/paragraphs/characters/lines, will also generate lists for repeated words, repeated phrases, adverbs (words that tend to end with “ly” – a big no-no for writers) and sentences that start with the same words? It would need some simple filtering so “and” “the” and similar words can be omitted from the search field. There are probably other lists it could compile, but these are the tools I can use most.
To be compatible with different document formats, it would probably work best if it were a standalone program that imported the document for the searches, but it would only generate lists – the user would then look for the words and phrases and make corrections in the original document. This could also be a useful plug-in for a word processor or office suite, but I've never actually tried to use a plug-in with Word, WordPerfect or LibreOffice, the programs I use most, and I don't even know if they would utilize a plug-in.
After writing the above, but before posting, I did a web search and found a more comprehensive filtering program than what I've described - SmartEdit by Bad Wolf Software. Pretty pricey at $49. I didn't find anything else out there with these basic search parameters. There are programs like Word Counter for Mac by Supermagnus Software, but it is more a word counter than a phrase and sentence start tool. And I'm not on a Mac.