Occasionally machine translation is good enough to be posted, so it shouldn't be blocked, but often it isn't good enough. If the software sees that the % of MT is high, a change tag can be added so that it would be easier for patrolers to check for this.
This type of content is already added to a category (T190798). This ticket proposes to add a specific edit tag in addition. This will allow more detailed analytics by differentiating articles originally published with too much MT (those with the tag) from those that still are considered as such (still in the category)
Result
In the list of tags for any Wikipedia (e.g., English Wikipedia Tags) you can find the contenttranslation-high-unmodified-mt-text which can be used in query and filtering tools such as Recent Changes to analyze the corresponding edits.
Related: T135707.