Comment by troupo

E.g. Google said in their document https://docs.google.com/document/d/1RC-pBBvsazYfCNNUSkPqAVpS...

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As a general rule of thumb, 0.1% of PageVisits (1 in 1000) is large, while 0.001% is considered small but non-trivial. Anything below about 0.00001% (1 in 10 million) is generally considered trivial. There are around 771 billion web pages viewed in Chrome every month (not counting other Chromium-based browsers). So seriously breaking even 0.0001% still results in someone being frustrated every 3 seconds, and so not to be taken lightly!

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Read the full doc. They even give examples when they couldn't remove a feature impacting just 0.0000008% of web views.