Not really. Maybe some products have an attribute that others don't. Maybe you want to query by that attribute. The query won't turn up products without that attribute. Maybe that's ok. Like if you wanted to find all shoes with black laces you can just query for that. Tractors don't even have laces and so they don't come up in the results.

In a sql db, every single thing needs to fit into a flat schema with nesting done by relations. Additionally, it's very rigid. Maybe you just don't want to set up a laces table, and 4000 other tables for every little attribute of every product. Of course this is not how you would do it in real life, there are better ways. Mongo is one of those ways.

Saying that Mongo is good for nothing is just as dumb as saying that Mongo is good for everything. In 2015, the Mongo backlash is just as tired as the Mongo hype.