limits of number of collections in databases

Question

Can anyone say are there any practical limits for the number of collections in mongodb? They write here https://docs.mongodb.com/manual/core/data-model-operations/#large-num

Answer 1

There seems to be a massive overhead for maintaining collections. I've just reduced a database which had around 1.5mio documents in 11000 collections to one with the same number of documents in around 300 collections; this has reduced the size of the database from 8GB to 1GB. I'm not familiar with the inner workings of MongoDB so this may be obvious but I thought might be worth noting in this context.