It's possible that the author did take this into consideration and glossed over the details, but it's not something that I as a reader take for granted. And it's not something that I as a coworker would take someone's word for, especially if they didn't list at least some examples of the things being removed.
Not trying to pile on the author. Trimming the fat on a codebase is great, and for sure a worthwhile exercise that not enough organizations pay mind to.
The 0.1% and 99.9% are not complements!
"Data driven" development is so much BS since so many devs don't care to think properly about sampling and statistics.
Never the less, my favorite thing to do with code is running over it with the delete key. Just be careful about what gets it ;-)
And this is why the users are the ultimate deciders - or at least should be - what features ought to be removed, rather than the developers.
> web application that serves hundreds of thousands of requests every day
So in this case, that's at least hundreds of requests per day. I mean, it's not small.
I agree completely with this comment, and another comment saying that "which percent contains the value of the product", because that might be the most important 0.1%.
For instance, I didn't delete the "Account Settings" page. Features don't need a high percentage of traffic to be important, but less important features generally account for a very low percentage of traffic.
I don't know about the author's application, but a data driven approach is not going to give good results. In my podcast hosting software, the "delete podcast" button is used maybe once every other week (by the numbers). But if I got rid of it, I'd be fielding support requests for every user who wants to delete a show. And that's a highly manual cleanup process to do by hand.
Which is to say, features don't need to be a high percentage of traffic to be important.