Wouldn't that allow to switch from Mongo to Postgres without having to rewrite all of your app?
As Op said, not needing to rewrite applications or using the muscle memory from using Mongo is beneficial. I'm not planning to be strict and support only MongoDB API; I will extend it when needed (e.g. to support raw SQL or JSON Path). But I plan to keep shim with compliant API for the above reasons.
MongoDB API has its quirks but is also pretty powerful and widely used.
I personally can't stand mongodb, its given me alot of headaches, joined a company and the same week I joined we lost a ton of data and the twat who set it up resigned in the middle of the outage. Got it back online and spend 6m moving to postgresql.