The Pre-Aggregated Reports use case:
https://docs.mongodb.org/ecosystem/use-cases/pre-aggregated-reports/
contains warnings and issues that are MMAPv1-specific without any indication that the issue does not affect WiredTiger.

For example:

There are, however, significant issues with this approach. The most significant issue is that, as you upsert data into the hourly and minute fields, the document grows. Although MongoDB will pad the space allocated to documents, it will need to reallocate these documents multiple times throughout the day, which impacts performance.

This will create confusion on whether padding issues are still relevant on WiredTiger.

Also, pointing people to this documentation could give the impression that the docs are not maintained since WiredTiger is available for a while already.